Photonic crystal element

Abstract

To provide a composite substrate capable of achieving a photonic crystal element with excellent characteristics.SOLUTION: A composite substrate for photonic crystal element comprises: an electrooptical crystal substrate having electrooptic effect; an optical loss inhibiting and cavity processing layer provided one on surface of the electrooptical crystal substrate; and a support substrate formed integrally with the electrooptical crystal substrate via the optical loss inhibiting and cavity processing layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a composite substrate for a photonic crystal device. [Background technology]

[0002] Various electro-optical elements are known. Electro-optical elements can convert electrical signals into optical signals by utilizing the electro-optic effect. Electro-optical elements are employed, for example, in radio-on-fiber communications, and their development is underway to achieve high-speed, high-capacity communications, low power consumption (low driving voltage), and a small footprint. An electro-optical element is configured, for example, using a composite substrate. A composite substrate typically includes an electro-optical crystal substrate having an electro-optic effect and a support substrate bonded to the electro-optical crystal substrate. This allows the electro-optical crystal substrate to be made thinner, and application development to achieve the various functions listed above has been active. In conventional composite substrates, the electro-optical crystal substrate and the support substrate are bonded together with an adhesive. With this configuration, peeling of the composite substrate may occur due to deterioration of the adhesive over time, and such peeling may further cause damage (e.g., cracks) to the electro-optical crystal substrate.

[0003] To address these issues, technologies have been developed that directly bond an electro-optic crystal substrate to a support substrate without using adhesives. However, when an electro-optic crystal substrate and a support substrate are directly bonded, an amorphous layer composed of elements from the electro-optic crystal substrate and the support substrate is formed between the two. This amorphous layer is not crystalline and has different optical properties from the electro-optic crystal substrate and the support substrate. Furthermore, the interface between the electro-optic crystal substrate and the amorphous layer is not flat. This uneven interface can cause scattering (e.g., diffuse reflection, leakage) and / or absorption of light traveling through the electro-optic crystal substrate. Furthermore, this amorphization can degrade the electro-optic effect of the electro-optic crystal, potentially preventing the desired low driving voltage from being achieved. To address these issues, technologies have been proposed, such as interposing a low-refractive-index layer between the electro-optic crystal substrate and the support substrate.

[0004] Meanwhile, photonic crystal elements are being developed as electro-optical elements. Photonic crystal elements are expected to be applied and developed in a wide range of fields, including optical waveguides, next-generation high-speed communications, sensors, laser processing, and solar power generation. Along with the development of such photonic crystal elements, composite substrates suitable for photonic crystal elements are desired. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6650551 Summary of the Invention [Problem to be solved by the invention]

[0006] A primary object of the present invention is to provide a composite substrate that can realize a photonic crystal element having excellent characteristics. [Means for solving the problem]

[0007] A composite substrate for a photonic crystal element according to an embodiment of the present invention comprises an electro-optic crystal substrate having an electro-optic effect, an optical loss suppression and cavity processing layer provided on one surface of the electro-optic crystal substrate, and a support substrate integrated with the electro-optic crystal substrate via the optical loss suppression and cavity processing layer. In one embodiment, the optical loss suppression and cavity processing layer is a single layer. In this embodiment, the photonic crystal device composite substrate may further include a peeling prevention layer between the electro-optic crystal substrate and the optical loss suppression and cavity processing layer. In this embodiment, the photonic crystal device composite substrate may further include a bonding layer between the optical loss suppression and cavity processing layer and the support substrate. In this embodiment, the photonic crystal device composite substrate may have a patterned sacrificial layer formed on the optical loss suppression and cavity processing layer. In this embodiment, the photonic crystal device composite substrate may further include an overcoat layer between the optical loss suppression and cavity processing layer and the support substrate. In another embodiment, the optical loss suppression and cavity processing layer comprises an optical loss suppression layer provided on the electro-optic crystal substrate and a cavity processing layer provided on the support substrate, and the optical loss suppression layer and the cavity processing layer are directly bonded to each other. In this embodiment, the photonic crystal device composite substrate may further include a bonding layer between the optical loss suppression layer and the support substrate. In this embodiment, the photonic crystal device composite substrate may have a patterned sacrificial layer formed on the optical loss suppression layer or the cavity processed layer. In this embodiment, the photonic crystal device composite substrate may further include an overcoat layer between the optical loss suppression layer and the cavity processed layer. According to another aspect of the present invention, there is provided a photonic crystal element using the above-mentioned composite substrate for photonic crystal elements. The photonic element comprises a photonic crystal layer formed by periodically forming holes in the electro-optic crystal substrate, a junction provided below the photonic crystal layer and integrating the photonic crystal layer with a support substrate, and a cavity defined by the lower surface of the photonic crystal layer, the upper surface of the support substrate, and the junction. In one embodiment, the photonic crystal device is constructed using the photonic crystal device composite substrate. In one embodiment, the photonic crystal layer has an etching through-hole formed therein, in which case the size of the etching through-hole may be larger than the size of the hole. [Effects of the Invention]

[0008] According to an embodiment of the present invention, in a composite substrate for a photonic crystal element having an electro-optic crystal substrate and a support substrate, an optical loss suppression and cavity processing layer is provided on one surface of the electro-optic crystal substrate, and the electro-optic crystal substrate and the support substrate are integrated via this optical loss suppression and cavity processing layer, thereby realizing a photonic crystal element with excellent characteristics. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic perspective view of a composite substrate for a photonic crystal device according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of the photonic crystal device composite substrate of FIG. [Figure 3] FIG. 10 is a schematic cross-sectional view of a composite substrate for a photonic crystal device according to another embodiment of the present invention. [Figure 4] FIG. 10 is a schematic cross-sectional view of a composite substrate for a photonic crystal device according to yet another embodiment of the present invention. [Figure 5] FIG. 10 is a schematic cross-sectional view of a composite substrate for a photonic crystal device according to yet another embodiment of the present invention. [Figure 6] 6A to 6C are schematic cross-sectional views illustrating a method for manufacturing the photonic crystal device composite substrate of FIG. 5. [Figure 7] FIG. 10 is a schematic cross-sectional view of a composite substrate for a photonic crystal device according to yet another embodiment of the present invention. [Figure 8] FIG. 10 is a schematic cross-sectional view of a composite substrate for a photonic crystal device according to yet another embodiment of the present invention. [Figure 9] FIG. 10 is a schematic cross-sectional view of a composite substrate for a photonic crystal device according to yet another embodiment of the present invention. [Figure 10] 1 is a schematic perspective view of a photonic crystal element according to one embodiment of the present invention. [Figure 11] 11(a) to 11(c) are schematic cross-sectional views illustrating an example of a method for manufacturing a photonic crystal element according to an embodiment of the present invention. [Figure 12] 12(a) to 12(d) are schematic cross-sectional views illustrating another example of a method for manufacturing a photonic crystal element according to an embodiment of the present invention. [Figure 13] 13(a) to 13(d) are schematic cross-sectional views illustrating yet another example of the method for manufacturing a photonic crystal element according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0011] A. Composite substrate for photonic crystal devices A-1. Overall configuration and variations FIG. 1 is a schematic perspective view of a composite substrate for photonic crystal devices (hereinafter sometimes simply referred to as a composite substrate) according to one embodiment of the present invention; and FIG. 2 is a schematic cross-sectional view of the composite substrate of FIG. 1. The composite substrate according to the embodiment of the present invention can typically be manufactured in the form of a wafer, as shown in FIG. 1. The composite substrate may be provided to the manufacturer of photonic crystal devices in the form of a wafer as shown in FIG. 1, or may be provided to the manufacturer in the form of a wafer (photonic crystal wafer) on which a photonic crystal layer is formed, as described below. In this specification, a photonic crystal wafer may be referred to as a photonic crystal device. That is, in this specification, the term "photonic crystal device" encompasses both a photonic crystal wafer and chips obtained by cutting the photonic crystal wafer.

[0012] The illustrated composite substrate 100 includes an electro-optic crystal substrate 10 having an electro-optic effect, an optical loss suppression and void processing layer 20 provided on one surface of the electro-optic crystal substrate, and a support substrate 30 integrated with the electro-optic crystal substrate 10 via the optical loss suppression and void processing layer 20. In the illustrated embodiment, the electro-optic crystal substrate 10 and the support substrate 30 are integrated by directly bonding the optical loss suppression and void processing layer 20 to the support substrate 30. An amorphous layer (not shown) is typically formed at the direct bonding interface. In the illustrated embodiment, the amorphous layer is a layer formed at the direct bonding interface between the optical loss suppression and void processing layer 20 and the support substrate 30. As the name suggests, the amorphous layer has an amorphous structure and is composed of elements constituting the optical loss suppression and void processing layer 20 and elements constituting the support substrate 30. 1 and 2, an amorphous layer may typically be formed at the bonding interface of a direct bond. The amorphous layer is composed of the constituent elements of the layers or substrates that are directly bonded to each other.

[0013] As described below, holes are formed in a predetermined pattern in the electro-optic crystal substrate 10 to form a photonic crystal layer in the photonic crystal device. The optical loss suppression and cavity processing layer 20 prevents an amorphous layer from being formed in the electro-optic crystal substrate during direct bonding, thereby suppressing optical loss in the electro-optic crystal substrate. After fulfilling its optical loss suppression function during direct bonding, the layer is removed by etching to form cavities in the photonic crystal device. Furthermore, by adjusting the constituent materials, thickness, etc., of the optical loss suppression and cavity processing layer 20, etching (typically dry etching) can be stopped at an appropriate level.

[0014] By directly bonding the electro-optic crystal substrate 10 and the support substrate 30 together, peeling of the composite substrate can be effectively suppressed, and as a result, damage (e.g., cracks) to the electro-optic crystal substrate due to such peeling can be effectively suppressed. Furthermore, by directly bonding the optical loss suppression and cavity processing layer 20 to the support substrate 30, direct bonding between the electro-optic crystal substrate and the support substrate can be avoided, thereby preventing the formation of an amorphous layer in the electro-optic crystal substrate. As a result, deterioration of the optical properties or optical loss of the electro-optic crystal substrate can be suppressed.

[0015] In this specification, "direct bonding" means that the components of the composite substrate (in the examples of FIGS. 1 and 2, the optical loss suppression and cavity processing layer 20 and the support substrate 30) are bonded together without the use of 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 -6A neutralization beam is irradiated onto the bonding surfaces of the components (layers or substrates) to be bonded at a pressure of about 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 this 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 a 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) and 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 used.

[0016] The optical loss suppression and cavity processing layer may be a single layer as described above, or may have an optical loss suppression layer and a cavity processing layer as described below. That is, the optical loss suppression and cavity processing layer may have both the optical loss suppression function and the cavity forming function as a single layer, or may be separated into two layers, the optical loss suppression layer and the cavity processing layer, and share the functions.

[0017] Modified examples of the composite substrate will be described below. The specific configurations of the components (layers or substrates) of the composite substrate will be described later in sections A-2 to A-8.

[0018] FIG. 3 is a schematic cross-sectional view of a composite substrate according to another embodiment of the present invention. In the illustrated composite substrate 100a, a delamination prevention layer 40 is provided between the electro-optic crystal substrate 10 and the optical loss suppression and void processing layer 20, and an overcoat layer 50 and a bonding layer 60 are provided between the optical loss suppression and void processing layer 20 and the support substrate 30. The bonding layer 60 may be directly bonded to the support substrate 30 and / or an adjacent layer on the opposite side of the support substrate 30 (the overcoat layer 50 or the optical loss suppression and void processing layer 20 in the illustrated example). Bonding layers may also be provided on the support substrate 30 and the overcoat layer 50 or the optical loss suppression and void processing layer 20, and these bonding layers may be directly bonded to each other. The provision of the delamination prevention layer 40 can prevent delamination between the electro-optic crystal substrate 10 and the adjacent layer (the optical loss suppression and void processing layer 20 in the illustrated example). The overcoat layer 50 may be provided as a layer to smooth out any unevenness in the optical loss suppression and void processing layer 20. Specifically, when a sacrificial layer 70 is formed as shown in FIG. 4 (described later), the sacrificial layer 70 and the optical loss suppression and cavity processing layer 20 are formed in separate processes, which may result in unevenness on the underside of the illustrated example. Forming an overcoat layer 50 in this case allows the surface to be formed as a single layer, facilitating planarization. Furthermore, providing a bonding layer 60 enables strong integration between the electro-optic crystal substrate 10 and the support substrate 30. The peel-prevention layer 40, the overcoat layer 50, and the bonding layer 60 are optional layers that are provided as needed, and at least one of them may be omitted. In the illustrated example, for example, the overcoat layer 50, the peel-prevention layer 40 and the overcoat layer 50, or the overcoat layer 50 and the bonding layer 60 may be omitted. When a bonding layer is present, an amorphous layer may be formed at the direct bonding interface between the bonding layer and an adjacent layer (including the direct bonding interface between bonding layers). When the overcoat layer and the bonding layer are omitted, similarly to FIG. 2, optical loss suppression and cavity processing layer 20 and supporting substrate 30 may be directly bonded together, and an amorphous layer may be formed at the bonding interface.

[0019] FIG. 4 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. In the illustrated composite substrate 100b, a sacrificial layer 70 is formed on the optical loss suppression and void processing layer 20. By providing the sacrificial layer 70, cavities for effectively realizing the functions of the photonic crystal can be easily formed in a desired shape. The cavities preferably have a sufficient thickness throughout the entire area directly below the holes of the photonic crystal. For this reason, the sacrificial layer 70 is formed in a predetermined pattern according to the purpose. In the illustrated embodiment, the sacrificial layer 70 is typically formed in a pattern and shape corresponding to the cavities in the photonic crystal element. In the illustrated embodiment, an overcoat layer 50 and / or a bonding layer 60 may be further provided between the optical loss suppression and void processing layer 20 (sacrificial layer 70) and the support substrate 30, as needed. When the bonding layer 60 is provided separately, the bonding layer 60 can be directly bonded to the optical loss suppression and void processing layer 20 (sacrificial layer 70) and / or the support substrate 30. When the overcoat layer 50 and the bonding layer 60 are provided, the overcoat layer 50 is typically provided on the sacrificial layer 70 side. The bonding layer 60 can be directly bonded to the overcoat layer 50 and / or the supporting substrate 30. As in the above embodiment, a bonding layer may be provided on each of the layers or substrates to be bonded, and the bonding layers may be directly bonded to each other.

[0020] FIG. 5 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. In the illustrated composite substrate 100c, the optical loss suppression and cavity processing layer includes an optical loss suppression layer 21 and a cavity processing layer 22. Typically, the optical loss suppression layer 21 is formed on the electro-optic crystal substrate 10, and the cavity processing layer 22 is formed on the support substrate 30. Typically, as shown in FIG. 6, the optical loss suppression layer 21 in the laminate of the optical loss suppression layer 21 / electro-optic crystal substrate 10 and the cavity processing layer 22 in the laminate of the cavity processing layer 22 / support substrate 30 are directly bonded to form a laminate structure of the optical loss suppression layer 21 and the cavity processing layer 22. The laminate structure of the optical loss suppression layer 21 and the cavity processing layer 22 can suppress damage to the electro-optic crystal layer due to etching of the cavity processing layer and / or can prevent holes from penetrating the cavity processing layer and reaching the support substrate during fabrication of the photonic crystal structure. Furthermore, it is possible to prevent foreign elements from diffusing into the electro-optic crystal substrate during processes such as bonding and etching.

[0021] 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 100d, an overcoat layer 50 and a bonding layer 60 are provided between the optical loss suppression layer 21 and the cavity processing layer 22. The overcoat layer 50 and the bonding layer 60 are optional layers that are provided as needed, and at least one of them may be omitted. In the illustrated embodiment, in many cases, only the bonding layer 60 may be provided. The bonding layer 60 may be directly bonded to the cavity processing layer 22 and / or the adjacent layer on the opposite side of the cavity processing layer 22 (in the illustrated example, the overcoat layer 50 or the optical loss suppression layer 21). As in the above embodiment, a bonding layer may be provided in each of the layers to be bonded (in the illustrated example, the cavity processing layer 22 and the overcoat layer 50 or the optical loss suppression layer 21), and the respective bonding layers may be directly bonded to each other.

[0022] FIG. 8 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. In the illustrated composite substrate 100e, a sacrificial layer 70 is formed on the cavity processing layer 22. By employing a laminated structure of the optical loss suppression layer 21 and the cavity processing layer 22 and by forming the sacrificial layer 70 on the cavity processing layer 22, it is possible to advantageously form cavities at the designed positions and in the designed shapes. In the illustrated embodiment, a bonding layer 60 may be further provided between the optical loss suppression layer 21 and the cavity processing layer 22 (sacrificial layer 70) or between the cavity processing layer 22 (sacrificial layer 70) and the support substrate 30, as necessary. The bonding layer 60 may be directly bonded to at least one adjacent layer, as in the above-described embodiment, or a bonding layer may be provided on each of the layers to be bonded, and the respective bonding layers may be directly bonded to each other.

[0023] FIG. 9 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. In the illustrated composite substrate 100f, a sacrificial layer 70 is formed on the optical loss suppression layer 21. In the composite substrate 100f, the cavity processing layer 22 and the support substrate 30 may be directly bonded to each other. The use of a laminated structure of the optical loss suppression layer 21 and the cavity processing layer 22 and the formation of the sacrificial layer 70 on the optical loss suppression layer 21 provides the advantage of allowing cavities to be formed at the designed positions and in the designed shapes. This structure is effective when patterning the cavity processing layer 22 is difficult. In the illustrated embodiment, an overcoat layer 50 and / or a bonding layer 60 may be further provided between the optical loss suppression layer 21 (sacrificial layer 70) and the cavity processing layer 22, or between the cavity processing layer 22 and the support substrate 30, as necessary.

[0024] The above-described embodiments may be appropriately combined depending on the purpose, and / or the above-described embodiments may be modified in a manner well known in the art.

[0025] A-2. Electro-optic crystal substrate The electro-optic crystal substrate 10 has an upper surface exposed to the outside and a lower surface located within the composite substrate. In an embodiment of the present invention, part or all of the electro-optic crystal substrate 10 serves as an optical waveguide for transmitting light in a photonic crystal device manufactured from the composite substrate. The electro-optic crystal substrate 10 is made of a crystal of a material having an electro-optic effect. Specifically, the optical constant (e.g., refractive index) of the electro-optic crystal substrate 10 can change when an electric field is applied. In one embodiment, the c-axis of the electro-optic crystal substrate 10 can be parallel to the electro-optic crystal substrate 10. That is, the electro-optic crystal substrate 10 can be an X-cut substrate or a Y-cut substrate. In another embodiment, the c-axis of the electro-optic crystal substrate 10 can be perpendicular to the electro-optic crystal substrate 10. That is, the electro-optic crystal substrate 10 can be a Z-cut substrate. The thickness of the electro-optic crystal substrate 10 can be set to any appropriate thickness depending on the frequency and wavelength of the electromagnetic wave used. The thickness of the electro-optic crystal substrate 10 can be, for example, 0.1 μm to 10 μm, or, for example, 0.1 μm to 3 μm. As will be described later, the composite substrate is reinforced by a support substrate, so the thickness of the electro-optic crystal substrate can be made thin.

[0026] Any appropriate material can be used to form the electro-optic crystal substrate 10, as long as it can provide the effects of the present invention. Representative examples of such materials include dielectrics (e.g., ceramics). Specific examples include lithium niobate (LiNbO3:LN), lithium tantalate (LiTaO3:LT), potassium titanyl phosphate (KTiOPO4:KTP), potassium lithium niobate (KTiOPO4:KTP), and the like. x Li (1-x) NbO2:KLM), potassium niobate (KNbO3:KN), potassium tantalate niobate (KNb x Ta (1-x) O3:KTN), and a solid solution of lithium niobate and lithium tantalate.

[0027] A-3.Support board The support substrate 30 has an upper surface located within the composite substrate and a lower surface exposed to the outside. The support substrate 30 is provided to increase the strength of the composite substrate, thereby enabling the thickness of the electro-optic crystal substrate to be reduced. Any appropriate configuration can be adopted for the support substrate 30. Specific examples of materials that can be used to form the support substrate 30 include silicon (Si), glass, sialon (Si3N4-Al2O3), mullite (3Al2O3·2SiO2, 2Al2O3·3SiO2), aluminum nitride (AlN), silicon nitride (Si3N4), magnesium oxide (MgO), sapphire, quartz, quartz crystal, gallium nitride (GaN), silicon carbide (SiC), and gallium oxide (Ga2O3). It is preferable that the linear expansion coefficient of the material forming the support substrate 30 is as close as possible to the linear expansion coefficient of the material forming the electro-optic crystal substrate 10. This configuration can suppress thermal deformation (typically, warpage) of the composite substrate. Preferably, the linear expansion coefficient of the material constituting support substrate 30 is within a range of 50% to 150% of the linear expansion coefficient of the material constituting electro-optic crystal substrate 10. From this perspective, the support substrate may be made of the same material as electro-optic crystal substrate 10.

[0028] A-4. Optical loss suppression and cavity processing layers A-4-1. Single layer As described above, the optical loss suppression and cavity processing layer (single layer) 20 has an optical loss suppression function, a cavity processing function, and an etching stop function. Any appropriate configuration can be adopted for the optical loss suppression and cavity processing layer as long as it has these functions. Examples of materials that can be used to form the optical loss suppression and cavity processing layer (single layer) include silicon dioxide (SiO2), amorphous silicon (a-Si), polycrystalline silicon (i.e., excluding single crystal silicon), molybdenum, aluminum oxide (Al2O3), compounds of these materials, and mixtures of these materials. The thickness of the optical loss suppression and cavity processing layer (single layer) is, for example, 0.1 μm to 1.0 μm, or, for example, 0.5 μm to 1.0 μm.

[0029] A-4-2.Layer structure of optical loss suppression layer and cavity processing layer When the optical loss suppression and cavity processing layer includes the optical loss suppression layer 21 and the cavity processing layer 22, the optical loss suppression layer may have any suitable configuration as long as it has an optical loss suppression function. Examples of materials that can be used for the optical loss suppression layer include amorphous silicon, polycrystalline silicon (i.e., excluding single-crystal silicon), molybdenum, aluminum oxide, compounds of these materials, and mixtures of these materials. The thickness of the optical loss suppression layer is, for example, 0.01 μm (10 nm) to 0.1 μm (100 nm), or, for example, 0.01 μm (10 nm) to 0.05 μm (50 nm).

[0030] The cavity processing layer may have any suitable structure as long as it has a cavity processing function and an etching stop function. Examples of materials that can be used for the cavity processing layer include silicon oxide, amorphous silicon, polycrystalline silicon, single-crystal silicon, molybdenum, aluminum oxide, compounds of these materials, and mixtures of these materials. The thickness of the cavity processing layer is, for example, 0.1 μm to 1.0 μm, or, for example, 0.3 μm to 0.7 μm.

[0031] A-5. Anti-peeling layer As described above, the peel-preventing layer 40 is provided to prevent or suppress peeling between the electro-optic crystal substrate 10 and an adjacent layer (typically, the optical loss suppression and cavity processing layer 20). Any appropriate configuration can be adopted for the peel-preventing layer depending on the configuration of the electro-optic crystal substrate and the adjacent layer. Examples of materials that can be used to form the peel-preventing layer include amorphous silicon, tantalum oxide (Ta2O5), niobium oxide (Nb2O5), titanium oxide (TiO2), aluminum oxide, and hafnium oxide (HfO2). The thickness of the peel-preventing layer is, for example, 0.01 μm to 0.1 μm.

[0032] A-6. Overcoat layer As described above, the overcoat layer 50 is provided to suppress optical loss and to flatten the cavity processing layer 20 if it has any irregularities. The overcoat layer may have any suitable configuration depending on the purpose and the configuration of adjacent layers (e.g., sacrificial layers). Examples of materials that can be used to form 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.

[0033] A-7.Joining layer As described above, the bonding layer 60 is provided to increase the bonding strength and achieve a strong integration between the electro-optic crystal substrate and the support substrate. Any appropriate configuration can be adopted for the bonding layer depending on the configuration of the substrate or layer to be bonded. Examples of materials that can be used for the bonding layer include silicon oxide, amorphous silicon, tantalum oxide, alumina (Al2O3), hafnia (HfO2), Cr / Au, and Cr / Cu. The thickness of the bonding layer is, for example, 0.01 μm to 0.1 μm, or, for example, 0.01 μm to 0.05 μm.

[0034] A-8. Sacrificial layer As described above, the sacrificial layer 70 is provided to form a cavity at a designed position and in a designed shape. Any appropriate configuration can be adopted for the sacrificial layer depending on the purpose. Examples of materials that can be used to form the sacrificial layer include amorphous silicon, 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.

[0035] B. Photonic Crystal Devices B-1. Photonic crystal element configuration 10 is a schematic perspective view of a photonic crystal element according to one embodiment of the present invention. The illustrated photonic crystal element 200 comprises a photonic crystal layer 10a formed by periodically forming holes 12 in an electro-optic crystal substrate 10; a junction 20a provided below the photonic crystal layer 10a and integrating the photonic crystal layer 10a with a support substrate 30; and a cavity 80 defined by the lower surface of the photonic crystal layer 10a, the upper surface 30 of the support substrate, and the inner surface of the junction 20a. The cavity 80 is formed by etching away the optical loss suppression and cavity processing layer of the composite substrate described in Section A above, with the remaining optical loss suppression and cavity processing layer constituting the junction 20a.

[0036] The photonic crystal that constitutes the photonic crystal layer 10a is a multidimensional periodic structure consisting of a medium with a high refractive index and a medium with a low refractive index, with a period comparable to the wavelength of light, and has an optical band structure similar to the band structure of electrons. Therefore, by appropriately designing the periodic structure, it is possible to create a predetermined optical forbidden band (photonic band gap). A photonic crystal with a forbidden band functions as an object that neither reflects nor transmits light of a predetermined wavelength. When a line defect that disrupts the periodicity is introduced into a photonic crystal with a photonic band gap, a waveguide mode is formed within the frequency range of the band gap, making it possible to realize an optical waveguide that propagates light with low loss.

[0037] The photonic crystal shown in the figure is a so-called slab-type two-dimensional photonic crystal. A slab-type two-dimensional photonic crystal is a photonic crystal in which cylindrical or polygonal low-refractive-index pillars with a refractive index lower than that of the material constituting the thin slab are arranged in a thin slab of dielectric or semiconductor at an appropriate two-dimensional periodic interval corresponding to the intended and desired photonic bandgap, and the thin slab is further sandwiched between upper and lower claddings with a refractive index lower than that of the thin slab. In the illustrated example, the air holes 12 function as the low-refractive-index pillars, the portion 14 between the air holes 12, 12 in the electro-optic crystal substrate 10 functions as the high-refractive-index portion, the cavity 80 functions as the lower cladding, and the external environment (air) above the photonic crystal element 200 functions as the upper cladding. Portions of the electro-optic crystal substrate 10 where the periodic pattern of the air holes 12 is not formed become line defects, and these line defect portions form the optical waveguide 16.

[0038] The holes 12 may be formed in a periodic pattern as described above. The holes 12 are typically arranged to form a regular lattice. Any appropriate lattice shape may be adopted as long as it can achieve a predetermined photonic band gap. Typical examples include a triangular lattice and a square lattice. In one embodiment, the holes 12 may be through-holes. Through-holes are easy to form, and as a result, the refractive index can be easily adjusted. Any appropriate shape may be adopted as the shape of the holes (through-holes) in plan view. Specific examples include equilateral polygons (e.g., equilateral triangles, squares, regular pentagons, regular hexagons, and regular octagons), approximate circles, and ellipses. An approximate circle is preferred. The approximate circle has a major axis / minor axis ratio of preferably 0.90 to 1.10, more preferably 0.95 to 1.05. Note that the through-holes 12 may be low-refractive-index pillars (pillar-shaped portions made of a low-refractive-index material) as described above. However, through holes are easier to form, and because they are made of air, which has the lowest refractive index, the difference in refractive index between the through holes and the optical waveguide can be made larger. Also, the diameter of some holes may be different from the diameter of other holes.

[0039] The lattice pattern of the air holes can be appropriately set depending on the purpose and desired photonic band gap. In the illustrated example, air holes with a diameter d1 form a square lattice with a period P. The square lattice pattern is formed on both sides of the photonic crystal element, and an optical waveguide 16 is formed in the center where no lattice pattern is formed. The width of the optical waveguide 16 can be, for example, 1.01P to 3P (2P in the illustrated example) relative to the air hole period P. The number of air hole rows in the optical waveguide direction (hereinafter sometimes referred to as lattice rows) can be 3 to 10 rows (5 rows in the illustrated example) on each side of the optical waveguide. The air hole period P can satisfy, for example, the following relationship: (1 / 7)×(λ / n)≦P≦1.4×(λ / n) Here, λ is the wavelength (nm) of light introduced into the optical waveguide, and n is the refractive index of the electro-optic crystal substrate. The hole period P can be, specifically, 0.1 μm to 1 μm. In one embodiment, the hole period P can be equal to the thickness of the photonic crystal layer (electro-optic crystal substrate). The hole diameter d1 can be, for example, 0.1P to 0.9P relative to the hole period P. A desired photonic band gap can be obtained by appropriately adjusting the hole diameter d1, the hole period P, the number of lattice rows, the number of holes per lattice row, the thickness of the photonic crystal layer, the constituent material of the electro-optic crystal substrate (effectively the refractive index), the width of the line defect portion, and the width and height of the cavity (described later). Furthermore, similar effects can be obtained with electromagnetic waves other than light waves. Specific examples of electromagnetic waves include millimeter waves, microwaves, and terahertz waves.

[0040] The cavity 80 is formed by etching away the optical loss suppression and cavity-processed layer 20 of the composite substrate as described above, and can function as a lower cladding. The width of the cavity is preferably greater than the width of the optical waveguide. For example, the cavity 80 may extend from the optical waveguide 16 to the third lattice row. In the illustrated example, the cavity 80 extends from the optical waveguide 16 to the third lattice row. Light not only propagates within the optical waveguide, but also some of the optical energy may diffuse to lattice rows near the optical waveguide. Therefore, by providing a cavity directly below such lattice rows, propagation loss due to light leakage can be suppressed. From this perspective, the cavity may be formed over the entire area of ​​the hole-forming region. The height of the cavity is preferably 0.1 μm or more, more preferably 1 / 5 or more of the wavelength of the propagating light. With such a height, the thin plate slab functions as a photonic crystal, achieving an optical waveguide with higher wavelength selectivity and lower loss. The height of the cavity can be controlled by adjusting the thickness of the components (layers) other than the electro-optic crystal substrate and the support substrate in the composite substrate.

[0041] In one embodiment, etching through-holes 90 may be formed in the photonic crystal layer 10a. By forming the etching through-holes 90, the etching solution can be efficiently distributed throughout the entire region to be etched. As a result, the desired cavities can be formed more precisely. While a single etching through-hole is formed in the illustrated example, multiple etching through-holes (e.g., two, three, or four) may be formed. The etching through-hole may be formed, for example, at a position three or more lattice rows away from the optical waveguide. This configuration allows the etching solution to be efficiently distributed throughout the entire region to be etched without adversely affecting the photonic bandgap. The etching through-hole may also be formed, for example, on the input and / or output side of the end of the lattice pattern opposite the optical waveguide (i.e., at the corners of the photonic crystal layer). This configuration further effectively prevents adverse effects on the photonic bandgap. For example, when four etching through-holes are formed, they may be formed at the four corners of the photonic crystal layer. The size of the etching through-hole 90 is typically larger than the size of the holes 12. For example, the diameter d2 of the etching through-hole is preferably 5 times or more, more preferably 50 times or more, and even more preferably 100 times or more, the diameter d1 of the hole. On the other hand, d2 is preferably 1000 times or less than d1. If d2 is too small, the etching solution may not be distributed well over the entire area to be etched. If d2 is too large, it may have an adverse effect on the photonic band gap.

[0042] B-2. Method for manufacturing photonic crystal elements A representative example of a method for manufacturing a photonic crystal element will be briefly described with reference to FIGS. 11 to 13. FIGS. 11(a) to 11(c) are schematic cross-sectional views illustrating an example of a process for fabricating a photonic crystal element from a composite substrate. This example illustrates a process for fabricating a photonic crystal element from a composite substrate similar to the composite substrate of FIG. 4, as shown in FIG. 11(a). This composite substrate, unlike the composite substrate of FIG. 4, further includes a bonding layer 60 between the optical loss suppression and cavity processing layer 20 (sacrificial layer 70) and the support substrate 30. First, as shown in FIG. 11(b), holes 12 are formed in the electro-optic crystal substrate 10 by etching using a predetermined mask. The etching is typically dry etching (e.g., reactive ion etching). The holes 12 can be formed, for example, in a pattern such as that shown in FIG. 10. Note that the formation of etching through-holes is omitted in the drawings. Next, the electro-optic crystal substrate with the holes formed therein is brought into contact with (e.g., immersed in) a predetermined etching solution to etch the sacrificial layer 70. As a result, a cavity 80 is formed as shown in Fig. 11(c), and a photonic crystal element is obtained. If the etching mask used in forming the cavity and the sacrificial layer are made of the same material, the remainder of the mask and the sacrificial layer can be removed simultaneously by a single contact (e.g., immersion).

[0043] 12(a) to 12(d) are schematic cross-sectional views illustrating another example of a process for fabricating a photonic crystal element from a composite substrate. This example illustrates a process for fabricating a photonic crystal element from a composite substrate similar to the composite substrate of FIG. 5, as shown in FIG. 12(a). This composite substrate, unlike the composite substrate of FIG. 5, further includes a bonding layer 60 between the optical loss suppression layer 21 and the cavity processing layer 22. First, as shown in FIG. 12(b), holes 12 are formed in the electro-optic crystal substrate 10, the optical loss suppression layer 21, and the bonding layer 60 by dry etching (e.g., reactive ion etching) using a predetermined mask. Next, as shown in FIG. 12(c), predetermined portions of the cavity processing layer 22 are removed by wet etching (e.g., immersion in an etching solution). Finally, as shown in FIG. 12(d), the remaining optical loss suppression layer 21 and the bonding layer 60 are removed by wet etching (e.g., immersion in an etching solution). As a result, cavities 80 are formed, and a photonic crystal element is obtained.

[0044] 13(a) to 13(d) are schematic cross-sectional views illustrating yet another example of a process for fabricating a photonic crystal element from a composite substrate. This example illustrates a process for fabricating a photonic crystal element from a composite substrate similar to the composite substrate of FIG. 9, as shown in FIG. 13(a). This composite substrate, unlike the composite substrate of FIG. 9, further includes a bonding layer 60 between the cavity processing layer 22 and the support substrate 30. First, as shown in FIG. 13(b), holes 12 are formed in the electro-optic crystal substrate 10 by dry etching (e.g., reactive ion etching) using a predetermined mask. Next, as shown in FIG. 13(c), the sacrificial layer 70 is removed by wet etching (e.g., immersion in an etching solution). Subsequently, as shown in FIG. 13(d), the cavity processing layer 22 is removed by wet etching (e.g., immersion in an etching solution). As a result, cavities 80 are formed, resulting in a photonic crystal element. If the sacrificial layer and the cavity processing layer are made of the same material, the remainder of the sacrificial layer and the cavity processing layer can be removed simultaneously by a single contact (for example, immersion).

[0045] It goes without saying that processes other than those shown in the drawings can be used to fabricate photonic crystal elements. By appropriately combining the overall structure of the composite substrate, the materials constituting each layer of the composite substrate, masks, etching methods, etc., it is possible to form holes and cavities in an efficient manner with high precision, and to fabricate photonic crystal elements. [Example]

[0046] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0047] Example 1 1. Fabrication of composite substrates for photonic crystal devices An X-cut lithium niobate substrate with a diameter of 4 inches was prepared as the electro-optic crystal substrate, and a silicon substrate with a diameter of 4 inches was prepared as the support substrate. First, amorphous silicon (a-Si) was sputtered onto the electro-optic crystal substrate to form an optical loss suppression layer with a thickness of 20 nm. Meanwhile, silicon oxide was sputtered onto the support substrate to form a cavity-processed layer with a thickness of 0.5 μm, and a-Si was sputtered onto the cavity-processed layer to form a bonding layer with a thickness of 20 nm. Next, the surfaces of the optical loss suppression layer and the bonding layer were each polished using CMP to achieve an arithmetic mean roughness Ra of 0.3 nm or less. Next, the surfaces of the optical loss suppression layer and the bonding layer were cleaned, and then the optical loss suppression layer and the bonding layer were directly bonded to integrate the electro-optic crystal substrate and the support substrate. Direct bonding was performed as follows. 10 -6In a vacuum of the Pa range, the bonding surfaces of the electro-optic crystal substrate and the support substrate (the surfaces of the optical loss suppression layer and bonding layer) were irradiated with a high-speed Ar neutral atom beam (accelerating voltage 1 kV, Ar flow rate 60 sccm) for 70 seconds. After irradiation, the electro-optic crystal substrate and the support substrate were left to cool for 10 minutes, and then the bonding surfaces of the electro-optic crystal substrate and the support substrate were brought into contact and pressed with 4.90 kN for 2 minutes to bond the electro-optic crystal substrate and the support substrate. After bonding, the electro-optic crystal substrate was polished to a thickness of 0.5 μm, resulting in a composite substrate for photonic crystal devices similar to that shown in Figure 5 (except for the presence of a bonding layer between the optical loss suppression layer and the cavity-processing layer). No defects such as peeling were observed at the bonding interface in the resulting composite substrate for photonic crystal devices.

[0048] 2. Fabrication of photonic crystal devices A photonic crystal element was fabricated from the composite substrate for photonic crystal elements obtained above using a method corresponding to the manufacturing method shown in Figure 12. Specifically, the photonic crystal element was fabricated using the following procedure. First, a molybdenum (Mo) film was formed on the electro-optic crystal substrate as a metal mask. Next, a resin pattern with holes in a predetermined arrangement was formed on the metal mask by nanoimprinting. Specifically, as the hole pattern corresponding to the holes in the photonic crystal, ten lattice rows with holes of 444 nm diameter each were formed on the left and right sides in a planar view, with a period (pitch) of 550 nm in the optical waveguide direction and in the direction perpendicular to the optical waveguide direction. No holes were formed in the center in a planar view (this part will eventually become the optical waveguide). In addition, four holes (patterns of through holes for etching) with a diameter of 200 μm were formed in the corners in a planar view (on the input and output sides of the ends opposite the optical waveguides of the left and right lattice rows). Next, holes corresponding to the above pattern were formed in the Mo mask by etching with a Mo etching solution (a mixture of nitric acid, acetic acid, and phosphoric acid in a ratio of 10:15:1). The hole pattern and etching through-holes were then formed in the composite substrate by fluorine-based reactive ion etching using the patterned Mo mask. The composite substrate was then immersed in a buffered hydrofluoric acid (BHF) etching solution to remove the cavity-processing layer and form the cavities. The remaining Mo mask was then removed with the Mo etching solution. Finally, the composite substrate was immersed in approximately 10% diluted tetramethylammonium hydroxide (TMAH) to etch the optical loss suppression layer and bonding layer, resulting in the fabrication of a photonic crystal wafer. The resulting photonic crystal wafer was then diced to obtain photonic crystal devices. The optical waveguide length of the photonic crystal device was 10 mm. After dicing, the input and output end faces of the optical waveguide were polished.

[0049] The obtained photonic crystal element (chip) was cut in the thickness direction, and the cross section was observed under a microscope. It was found that a cavity was well formed directly below the photonic crystal layer. The yield of chips in which the cavity was formed as designed was 100%. Furthermore, the optical insertion loss of the obtained chip was measured. Specifically, light with a wavelength of 1.55 μm was introduced into the chip (effectively the optical waveguide of the photonic crystal layer) through the input-side bulb-tipped fiber coupled to the optical fiber, and the amount of light output through the output-side bulb-tipped fiber was measured with a photodetector to calculate the propagation loss. The propagation loss of the optical waveguide was 0.5 dB / cm.

[0050] <Example 2> 1. Fabrication of composite substrates for photonic crystal devices An electro-optic crystal substrate and a support substrate similar to those in Example 1 were prepared. Next, a Mo film (0.5 μm thick) was formed as a sacrificial layer on the electro-optic crystal substrate by sputtering. Note that Mo does not diffuse into the electro-optic crystal substrate (lithium niobate substrate) and therefore is believed not to cause optical degradation of the electro-optic crystal substrate. The sacrificial layer was then patterned by photolithography. Specifically, the sacrificial layer portion of the Mo film was covered with a resist mask pattern, and the exposed portion was removed with a Mo etchant. Next, silicon oxide was sputtered on the surface on which the Mo pattern was formed to form an optical loss suppression and cavity processing layer with a thickness of 1 μm, and the layer was polished by CMP to a surface roughness Ra of 0.3 nm or less. Furthermore, a-Si was sputtered on the surface of the polished layer to form a bonding layer with a thickness of 20 nm, and the bonding layer was polished by CMP to a surface roughness Ra of 0.3 nm or less. Next, the surfaces of the bonding layer and the support substrate were cleaned, and the bonding layer and the support substrate were directly bonded to each other to integrate the electro-optic crystal substrate and the support substrate. The conditions for direct bonding were the same as in Example 1. After bonding, the electro-optic crystal substrate was polished until its thickness was 0.5 μm, yielding a composite substrate for photonic crystal elements similar to that shown in Figure 4 (but with a bonding layer between the electro-optic crystal substrate and the support substrate). No defects such as peeling were observed at the bonding interface in the resulting composite substrate for photonic crystal elements.

[0051] 2. Fabrication of photonic crystal devices A photonic crystal element was fabricated from the composite substrate for photonic crystal elements obtained above using a method corresponding to the manufacturing method shown in FIG. 11. Specifically, the photonic crystal element was fabricated using the following procedure. First, a hole pattern and etching through-holes were formed in the same manner as in Example 1. Next, the composite substrate was immersed in a Mo etching solution to etch away the remaining Mo mask and the sacrificial layer, producing a photonic crystal wafer. The resulting photonic crystal wafer was cut into chips in the same manner as in Example 1, to obtain photonic crystal elements. The optical waveguide length of the photonic crystal element was 10 mm, the same as in Example 1. After cutting into chips, the end faces were polished in the same manner as in Example 1.

[0052] The obtained photonic crystal element (chip) was subjected to the same evaluation as in Example 1. As a result, it was found that a cavity was well formed directly below the photonic crystal layer, and the yield of chips in which the cavity was formed as designed was 100%. Furthermore, the propagation loss of the optical waveguide of the obtained chip was 0.5 dB / cm.

[0053] Example 3 1. Fabrication of composite substrates for photonic crystal devices An electro-optic crystal substrate and a support substrate similar to those in Example 1 were prepared. Next, a Mo film (0.215 μm thick) serving as an optical loss suppression layer was formed on the electro-optic crystal substrate by sputtering. Furthermore, the optical loss suppression layer was patterned by photolithography. Specifically, the portion of the Mo film that would become the optical loss suppression layer was covered with a resist mask pattern, and the exposed portion was removed with a Mo etchant. Next, silicon oxide was sputtered on the surface on which the Mo pattern was formed to form a 0.25 μm-thick sacrificial layer, which was then polished by CMP to a surface roughness Ra of 0.3 nm or less. Next, silicon oxide was sputtered on the polished surface of the sacrificial layer to form a 0.5 μm-thick cavity-processed layer, which was then polished by CMP to a surface roughness Ra of 0.3 nm or less. Furthermore, a-Si was sputtered to form a bonding layer with a thickness of 20 nm, which was then polished by CMP to a surface roughness Ra of 0.3 nm or less. The following procedure was carried out in the same manner as in Example 1 to obtain a composite substrate for photonic crystal elements (except that a bonding layer was present between the electro-optic crystal substrate and the support substrate) similar to that shown in Fig. 9. No defects such as peeling were observed at the bonding interface in the obtained composite substrate for photonic crystal elements.

[0054] 2. Fabrication of photonic crystal devices A photonic crystal element was fabricated from the composite substrate for photonic crystal elements obtained above using a method corresponding to the manufacturing method shown in FIG. 13. Specifically, the photonic crystal element was fabricated using the following procedure. First, a hole pattern and etching through-holes were formed in the same manner as in Example 1. Next, the composite substrate was immersed in a Mo etching solution to etch away the remaining Mo mask. The composite substrate was then immersed in a BHF etching solution to remove the sacrificial layer and cavity processing layer to form cavities, thereby producing a photonic crystal wafer. The resulting photonic crystal wafer was cut into chips in the same manner as in Example 1 to obtain photonic crystal elements. The optical waveguide length of the photonic crystal element was 10 mm, the same as in Example 1. After cutting into chips, the end faces were polished in the same manner as in Example 1.

[0055] The obtained photonic crystal element (chip) was subjected to the same evaluation as in Example 1. As a result, it was found that a cavity was well formed directly below the photonic crystal layer, and the yield of chips in which the cavity was formed as designed was 100%. Furthermore, the propagation loss of the optical waveguide of the obtained chip was 0.5 dB / cm.

[0056] Example 4 A composite substrate for photonic crystal devices was fabricated in the same manner as in Example 1, except that no through-holes for etching were formed. Photonic crystal wafers and photonic crystal devices (chips) were then fabricated from the composite substrate. The resulting photonic crystal devices (chips) were subjected to the same evaluation as in Example 1. As a result, chips were found in which no cavities were formed directly below the photonic crystal layer. The yield of chips in which cavities were formed as designed was approximately 50%. Furthermore, the propagation loss of the optical waveguide in chips in which cavities were formed was 0.5 dB / cm, while the propagation loss of the optical waveguide in chips in which cavities were not formed was 2 dB / cm or more. [Industrial Applicability]

[0057] The composite substrate according to the embodiment of the present invention can be suitably used in a photonic crystal element, which can be suitably used in a wide range of fields such as optical waveguides, next-generation high-speed communications, sensors, laser processing, and solar power generation. [Explanation of symbols]

[0058] 10 Electro-optic crystal substrate 12 Vacancies 14 Thin Plate Slab 16 Optical waveguide 20 Optical loss suppression and cavity processing layer 21 Optical loss suppression layer 22 Hollow processing layer 30 Support substrate 40 Anti-peeling layer 50 Overcoat layer 60 Bonding layer 70 Sacrificial Layer 80 hollow 90 Etching through hole 100 Composite substrate for photonic crystal devices 100a Composite substrate for photonic crystal element 100b Composite substrate for photonic crystal element 100c Composite substrate for photonic crystal devices 100d Composite substrate for photonic crystal devices 100e Composite substrate for photonic crystal devices 100f Composite substrate for photonic crystal devices 200 Photonic Crystal Device

Claims

1. an electro-optic crystal substrate having an electro-optic effect; a cavity processed layer provided on one surface of the electro-optic crystal substrate; a support substrate that is integrated with the electro-optic crystal substrate via the cavity processed layer; the cavity processing layer and the support substrate are directly bonded to each other, and an amorphous layer is formed between the cavity processing layer and the support substrate; The electro-optic crystal substrate has holes periodically formed therein to form a photonic crystal layer.

2. The photonic crystal element according to claim 1 , further comprising a peeling prevention layer between the electro-optic crystal substrate and the cavity processed layer.

3. The photonic crystal element according to claim 1 , further comprising a bonding layer between the cavity processed layer and the support substrate.

4. The photonic crystal element according to claim 1 , wherein a patterned sacrificial layer is formed on the cavity processing layer.

5. 5. The photonic crystal element according to claim 1, further comprising an overcoat layer between the cavity processed layer and the support substrate.

6. The cavity processed layer has a cavity formed therein to form a joining portion, the junction is provided below the photonic crystal layer and integrates the photonic crystal layer with the support substrate; The photonic crystal device according to claim 1 , wherein the cavity is defined by the lower surface of the photonic crystal layer, the upper surface of the support substrate, and the junction.

7. The photonic crystal element according to claim 1 , wherein the photonic crystal layer has through-holes for etching formed therein.

8. The photonic crystal element according to claim 7 , wherein the size of the etching through-hole is larger than the size of the air hole.

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