Composite substrate structure and preparation method thereof

Abstract

The invention discloses a composite substrate structure and a preparation method thereof, and the composite substrate structure comprises a first substrate which comprises a first surface and a second surface which are arranged oppositely, a photonic crystal structure is formed on the first surface, and the photonic crystal structure comprises a plurality of photonic crystal units which are periodically distributed at intervals, a first conductive film is formed on the surface of the photonic crystal unit; the second substrate comprises a third surface and a fourth surface which are arranged oppositely, and a second conductive film is formed on the third surface; the second substrate is located on the first substrate, and the second conductive film is bonded with the first conductive film. The first substrate is used as a supporting substrate, a photonic crystal structure is integrated on the supporting substrate, various optical functions from visible light to an infrared band are achieved, the first conductive film and the second conductive film are combined to serve as conductive non-metal middle layers, and optical and electrical properties are considered.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a composite substrate structure and its preparation method. Background Technology

[0002] With the rapid development of the global digital economy, low-power microelectronics with smaller feature widths and better architectures, as well as high-performance and highly integrated optoelectronics, are expected to alleviate the growing energy challenges.

[0003] For components such as low-loss waveguides, high-performance resonators, and high-efficiency couplers, wavelength selection and transmission control of light are required. Due to the weak interaction between photons and matter, photons are much more difficult to control than electrons.

[0004] In addition, lasers used for fiber optic communication and industrial processing are usually made of compound semiconductor materials such as GaAs and InP, but they suffer from insufficient laser power and lifespan.

[0005] Therefore, in order to address the above-mentioned technical problems, it is necessary to provide a composite substrate structure and its preparation method. Summary of the Invention

[0006] The purpose of this invention is to provide a composite substrate structure and its preparation method, which can realize a variety of optical functions from visible light to infrared bands, and can solve the problems of insufficient laser power and lifespan.

[0007] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0008] A composite substrate structure, comprising:

[0009] The first substrate includes a first surface and a second surface disposed opposite to each other. A photonic crystal structure is formed on the first surface. The photonic crystal structure includes a plurality of photonic crystal units distributed at periodic intervals. A first conductive thin film is formed on the surface of the photonic crystal unit.

[0010] The second substrate includes a third surface and a fourth surface disposed opposite to each other, wherein a second conductive thin film is formed on the third surface;

[0011] The second substrate is located on the first substrate, and the second conductive film is bonded to the first conductive film.

[0012] In one or more embodiments of the present invention, the first substrate is one of a diamond substrate, a SiC substrate, or a group V boride substrate; and / or,

[0013] The first substrate is a single-crystal substrate or a polycrystalline substrate.

[0014] In one or more embodiments of the present invention, the period of the photonic crystal structure is 100 nm to 5 μm, and the duty cycle is 0.05 to 0.95; and / or,

[0015] The thickness of the photonic crystal unit is 10 nm to 10 μm; and / or,

[0016] The side surface roughness of the photonic crystal unit is less than or equal to 5 nm.

[0017] In one or more embodiments of the present invention, the second substrate is a III-V compound substrate; and / or,

[0018] The thickness of the second substrate is 200 nm to 10 μm; and / or,

[0019] The surface roughness of the fourth surface is less than or equal to 0.5 nm.

[0020] In one or more embodiments of the present invention, the material of the first conductive film includes at least one selected from amorphous silicon, polycrystalline silicon, amorphous carbon, polycrystalline carbon, amorphous group III nitride, polycrystalline group III nitride, amorphous germanium, and polycrystalline germanium; and / or,

[0021] The thickness of the first conductive film is 1 nm to 50 nm; and / or,

[0022] The surface roughness of the first conductive film located on the upper surface of the photonic crystal unit is less than or equal to 0.5 nm.

[0023] In one or more embodiments of the present invention, the material of the second conductive film includes at least one selected from amorphous silicon, polycrystalline silicon, amorphous carbon, polycrystalline carbon, amorphous group III nitride, polycrystalline group III nitride, amorphous germanium, and polycrystalline germanium; and / or,

[0024] The thickness of the second conductive film is 1 nm to 50 nm; and / or,

[0025] The surface roughness of the second conductive film is less than or equal to 0.5 nm.

[0026] A specific embodiment of the present invention provides a method for preparing a composite substrate structure, the method comprising:

[0027] A first substrate is provided, the first substrate including a first surface and a second surface disposed opposite to each other;

[0028] A photonic crystal structure is fabricated on the first surface by photolithography and / or etching, the photonic crystal structure comprising a plurality of periodically spaced photonic crystal units;

[0029] A first conductive thin film is deposited on the surface of the photonic crystal structure;

[0030] A second substrate is provided, the second substrate including a third surface and a fourth surface disposed opposite to each other;

[0031] A second conductive thin film is deposited on the third surface of the second substrate;

[0032] The second conductive film is bonded to the first conductive film.

[0033] In one or more embodiments of the present invention, before fabricating a photonic crystal structure on the first surface, the root mean square roughness of the first surface is reduced to less than or equal to 0.3 nm by chemical mechanical polishing and / or argon plasma surface treatment.

[0034] In one or more embodiments of the present invention, bonding the first conductive film to the second conductive film includes:

[0035] In a vacuum environment, the photonic crystal structure of the first substrate and the third surface of the second substrate are simultaneously activated by an argon fast atom beam, wherein the energy of the argon fast atom beam is 0.5keV~2keV and the activation processing time is 100s~1000s.

[0036] The first conductive film and the second conductive film are bonded in a vacuum environment at room temperature, with a bonding pressure of 0.5 MPa to 50 MPa and a bonding pressure duration of 1 to 10 minutes.

[0037] In one or more embodiments of the present invention, after bonding the first conductive film to the second conductive film, the thickness of the second substrate is reduced to 200 nm to 10 μm, and the surface roughness of the fourth surface of the second substrate is processed to be less than or equal to 0.5 nm.

[0038] Compared with existing technologies, the composite substrate structure and its fabrication method of the present invention use a first substrate as a supporting substrate and integrate a photonic crystal structure on the supporting substrate to achieve multiple optical functions in the visible to infrared bands. Furthermore, by combining a first conductive film and a second conductive film as a conductive non-metallic interlayer, both optical and electrical properties are considered. The composite substrate structure of the present invention is geared towards advanced packaging and heterogeneous integration applications. Compared with epitaxial monolithic integration, the bonding-based composite substrate structure offers greater flexibility in material selection and combination, and richer functionality. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of a composite substrate structure in one embodiment of the present invention;

[0041] Figure 2 This is a flowchart of a method for preparing a composite substrate structure according to an embodiment of the present invention;

[0042] Figures 3a-3d This is another flowchart of a method for preparing a composite substrate structure according to an embodiment of the present invention. Detailed Implementation

[0043] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0044] To facilitate understanding of the technical solutions of this application, the technical terms that may appear in this invention will be explained in detail below.

[0045] III-V compounds: binary or multi-component compound semiconductor materials composed of elements from Group III (Group 13) and Group V (Group 15) of the periodic table. Common III-V compounds are composed of Al, Ga, In combined with N, P, As, Sb (e.g., GaAs, InP, AlN, etc.).

[0046] As mentioned in the background art, with the rapid development of the global digital economy, especially driven by generative artificial intelligence, the demand for computing power has increased exponentially. A large number of data centers have been newly built, and the huge data transmission and operation have brought huge energy consumption. Low-power microelectronic technologies with smaller feature line widths and better architectures, and optoelectronic technologies with high performance and high integration are expected to alleviate the growing energy challenges. Due to the weak interaction between photons and matter, photons are much more difficult to manipulate than electrons. Photonic crystals are a method of manipulating light by using the spatial periodic distribution of materials. Destructive interference at specific wavelengths produces photonic band gaps. Within the photonic band gap frequency range, light cannot propagate. By adjusting the photonic crystal structure, the dispersion relationship and conduction or radiation modes of light can be artificially customized. The special edge states and defect states of photonic crystals can be applied to components such as low-loss waveguides, high-performance resonators, and efficient couplers to perform wavelength selection and transmission control of light.

[0047] As the most common semiconductor material, the band gap of silicon is about 1.1 eV. The working optical wavelength range of silicon photonic crystals mainly focuses on the near-infrared band with a wavelength of 1100 nm, and these wavelengths have lower losses in silicon. The loss of silicon increases sharply at short wavelengths. For example, when the wavelength is less than 800 nm, the absorption increases significantly. For visible light and applications with shorter wavelengths, photonic crystal structures made of SiC with a band gap of 3.3 eV or other wide-bandgap materials are suitable. In addition, lasers used in optical fiber communication and industrial processing are usually made of compound semiconductor materials such as GaAs and InP. Integrating the laser on high-thermal-conductivity materials such as diamond (2000 W / mK) and SiC (300 W / mK) is beneficial to improving the power of the laser and increasing the lifespan of the laser.

[0048] See Figure 1 As shown, the present invention provides a composite substrate structure, including:

[0049] A first substrate 10, including a first surface and a second surface arranged opposite to each other. A photonic crystal structure is formed on the first surface. The photonic crystal structure includes a plurality of photonic crystal units 11 distributed at periodic intervals. A first conductive thin film 12 is formed on the surface of the photonic crystal unit 11.

[0050] A second substrate 20, including a third surface and a fourth surface arranged opposite to each other. A second conductive thin film 21 is formed on the third surface;

[0051] The second substrate 20 is located on the first substrate 10, and the second conductive thin film 21 is bonded to the first conductive thin film 12.

[0052] The composite substrate structure of the present invention is a composite substrate that combines high thermal conductivity diamond, silicon carbide and III-V compound semiconductor. A photonic crystal structure is integrated on the supporting substrate, which can realize a variety of optical functions from visible light to infrared band. The conductive non-metallic intermediate layer takes into account both optical and electrical performance.

[0053] The composite substrate structure of this invention integrates multiple functions, including electrical, optical, and thermal functions, and can be applied to advanced packaging and heterogeneous integration applications. Compared with epitaxial growth-based monolithic integration, the bonding-based composite substrate structure offers greater flexibility in material selection and combination, and richer functionality.

[0054] In one specific embodiment, the first substrate 10 is a high thermal conductivity substrate, such as a single-crystal diamond substrate, a polycrystalline diamond substrate, a single-crystal SiC substrate, a polycrystalline SiC substrate, a polycrystalline group V boride substrate, or a single-crystal group V boride substrate.

[0055] In one specific embodiment, the group V borides are BAs, BSb, etc.

[0056] The first substrate 10, by employing a high thermal conductivity substrate, can quickly conduct the heat generated by the device to the heat dissipation system, avoiding localized overheating and extending device lifespan. Furthermore, the first substrate 10 can support higher power densities, prevent performance degradation, and reduce the impact of temperature on carrier mobility, maintaining high-frequency stability.

[0057] In one specific embodiment, the period of the photonic crystal structure is 100 nm to 5 μm, and the duty cycle is 0.05 to 0.95. It is understood that a photonic crystal structure is a periodic structure material, composed of media with different refractive indices arranged periodically. The photonic crystal structure in this invention consists of periodically arranged air media and a first substrate 10 material medium.

[0058] In one specific embodiment, the thickness of the photonic crystal unit 11 is 10 nm to 10 μm, and the surface roughness of the side surface of the photonic crystal unit 11 is less than or equal to 5 nm. Further, the surface roughness of the upper surface of the photonic crystal unit 11 (i.e., the first surface of the first substrate 10) is less than or equal to 0.3 nm.

[0059] The photonic crystal structure of the present invention can realize a variety of optical functions from visible light to infrared bands, and the photonic crystal structure, as a conductive non-metallic intermediate layer that conforms to the substrate structure, takes into account both optical and electrical properties.

[0060] In one specific embodiment, the second substrate 20 is a III-V compound substrate, such as single-crystal GaAs, single-crystal InP, single-crystal GaSb, and single-crystal InAs.

[0061] In a specific embodiment, the thickness of the second substrate 20 is 200 nm to 10 μm.

[0062] In a specific embodiment, the surface roughness of the fourth surface of the second substrate 20 is less than or equal to 0.5 nm.

[0063] In a specific embodiment, both the first conductive thin film 12 and the second conductive thin film 21 are non-metal conductive thin films.

[0064] Specifically, the material of the first conductive thin film 12 includes at least one of amorphous silicon, polycrystalline silicon, carbon, group III nitrides, amorphous germanium, and polycrystalline germanium. The thickness of the first conductive thin film 12 is 1 nm to 50 nm.

[0065] The surface roughness of the first conductive thin film 12 on the upper surface of the photonic crystal unit 11 is less than or equal to 0.5 nm, that is, the surface roughness of the first conductive thin film 12 on the surface of the unetched first substrate is less than or equal to 0.5 nm.

[0066] The material of the second conductive thin film 21 includes at least one of amorphous silicon, polycrystalline silicon, carbon, group III nitrides, amorphous germanium, and polycrystalline germanium. The thickness of the second conductive thin film 21 is 1 nm to 50 nm, and the surface roughness of the second conductive thin film 21 is less than or equal to 0.5 nm.

[0067] The total thickness variation (TTV) between the first substrate 10 and the second substrate 10 is less than 5 μm.

[0068] Refer Figure 2 As shown, the present invention also provides a method for preparing a composite substrate structure, including:

[0069] S21, providing a first substrate 10, the first substrate 10 including a first surface and a second surface disposed opposite to each other.

[0070] In a specific embodiment, the first substrate 10 is a high thermal conductivity substrate. For example, the first substrate 10 is one of a single crystal diamond substrate, a polycrystalline diamond substrate, a single crystal SiC substrate, a polycrystalline SiC substrate, a polycrystalline group V boride substrate, or a single crystal group V boride substrate, and the group V boride is BAs, BSb, etc.

[0071] S22, preparing a photonic crystal structure on the first surface by photolithography and etching, the photonic crystal structure including a plurality of photonic crystal units 11 distributed at periodic intervals;

[0072] Combined Figure 3aAs shown, the period of the photonic crystal structure is 100 nm to 5 μm (i.e., the sum of the widths of k+c shown in the figure is 100 nm to 5 μm), and the duty cycle is 0.05 to 0.95. It can be understood that a photonic crystal structure is a periodic structure material, which is composed of media with different refractive indices arranged periodically. The photonic crystal structure in this invention consists of a periodically arranged air medium and a first substrate 10 material medium.

[0073] In one specific embodiment, the thickness of the photonic crystal unit 11 is 10 nm to 10 μm, and the surface roughness of the side surface of the photonic crystal unit 11 is less than or equal to 5 nm. Further, the surface roughness of the upper surface of the photonic crystal unit 11 (i.e., the first surface of the first substrate 10) is less than or equal to 0.3 nm.

[0074] Furthermore, before fabricating the photonic crystal structure on the first surface, the root mean square roughness of the first surface is reduced to less than or equal to 0.3 nm by chemical mechanical polishing and argon plasma surface treatment.

[0075] S23, deposit a first conductive thin film 12 on the surface of the photonic crystal structure.

[0076] Combination Figure 3b As shown, the first conductive film 12 is a non-metallic conductive film. The material of the first conductive film 12 includes at least one of amorphous silicon, polycrystalline silicon, carbon, group III nitride, amorphous germanium, and polycrystalline germanium. The deposition thickness of the first conductive film 12 is 1 nm to 50 nm, and the surface roughness of the first conductive film 12 is less than or equal to 0.5 nm.

[0077] Understandably, the first conductive film 12 completely covers the surface of the photonic crystal structure.

[0078] S24, a second substrate 20 is provided, the second substrate 20 including a third surface and a fourth surface disposed opposite to each other.

[0079] In one specific embodiment, the second substrate 20 is a III-V compound substrate, such as single-crystal GaAs, single-crystal InP, single-crystal GaSb, and single-crystal InAs.

[0080] S25, a second conductive thin film 21 is deposited on the third surface of the second substrate 20.

[0081] Combination Figure 3c As shown, in one specific embodiment, the material of the second conductive film 21 includes at least one of amorphous silicon, polycrystalline silicon, carbon, group III nitride, amorphous germanium, and polycrystalline germanium. The thickness of the second conductive film 21 is 1 nm to 50 nm, and the surface roughness of the second conductive film 21 is less than or equal to 0.5 nm.

[0082] S26. Bond the second conductive thin film 21 to the first conductive thin film 12.

[0083] In a specific embodiment, bonding the first conductive thin film 12 to the second conductive thin film 21 specifically includes:

[0084] S261. In a vacuum environment, simultaneously activate the photonic crystal structure of the first substrate 10 and the third surface of the second substrate 20 through an argon fast atom beam. Among them, the energy of the argon fast atom beam is 0.5 keV to 2 keV, and the activation treatment time is 100 s to 1000 s. Preferably, the vacuum environment is in a vacuum chamber with a vacuum degree greater than or equal to 1E-5 Pa.

[0085] S262. Bond the first conductive thin film 12 to the second conductive thin film 21 in a room temperature vacuum environment, with a bonding pressure of 0.5 MPa to 50 MPa, and the duration of the bonding pressure is 1 to 10 minutes.

[0086] Refer Figure 3d As shown, after bonding the first conductive thin film 12 to the second conductive thin film 21, thin the thickness of the second substrate 20 to 200 nm to 10 μm, and process the surface roughness of the fourth surface of the second substrate 20 to be less than or equal to 0.5 nm.

[0087] In a specific embodiment, the second substrate 20 is thinned by using a method of chemical etching and chemical mechanical polishing.

[0088] The present invention will be further described below in conjunction with specific embodiments.

[0089] Example 1:

[0090] This example provides a preparation method for a composite substrate structure, including:

[0091] Provide a 6-inch 4H-SiC(0001) (the first substrate), and process the root mean square roughness of the 4H-SiC(0001) surface to 0.3 nm by combining chemical mechanical polishing and argon plasma bombardment;

[0092] Use electron beam lithography and dry etching on 4H-SiC to fabricate a photonic crystal structure with a resonant wavelength of 800 nm. The lattice constant of the photonic crystal structure is 240 nm, the duty cycle is 0.35 (that is, the width of the air medium in this example is 85 nm), the etching depth is 200 nm, and the sidewall roughness is 3 nm.

[0093] Provide a 6-inch GaAs(001) substrate (the second substrate);

[0094] On the surface of the photonic crystal structure and the GaAs(001) substrate, a polycrystalline AlN layer (i.e., the first conductive film and the second conductive film) with a thickness of 30 nm was deposited by reactive sputtering. The root mean square roughness of the surface after AlN deposition in the non-etched region of 4H-SiC(0001) and the root mean square roughness of the surface after AlN deposition on the GaAs(001) substrate were both 0.5 nm. The total thickness deviation between the SiC and GaAs substrates was 3 μm.

[0095] In a vacuum chamber with a vacuum level of 3E-5Pa, the surfaces of SiC substrates and GaAs substrates with photonic crystal structures were simultaneously activated by argon fast atom beams. The processing time was 600s at an argon atom beam energy of 1.5keV. Subsequently, vacuum bonding was performed at room temperature with a bonding pressure of 2MPa and a holding pressure of 3 minutes.

[0096] The GaAs substrate was chemically etched using NH4OH-H2O2 and C6H8O7-H2O2 solutions, and then chemically and mechanically polished to reduce the GaAs substrate to a thickness of 1 μm with a surface roughness of less than or equal to 0.5 nm.

[0097] This embodiment also provides a composite substrate structure obtained based on the above preparation method.

[0098] Example 2:

[0099] This embodiment provides a method for preparing a composite substrate structure, including:

[0100] Provides 2-inch CVD diamond (first substrate) and 2-inch InP(001) substrate (second substrate);

[0101] The root mean square roughness of the CVD diamond surface was reduced to 0.2 nm by combining chemical mechanical polishing and argon plasma bombardment.

[0102] Deep ultraviolet lithography and dry etching CVD diamond were used to fabricate a photonic crystal structure with a resonant wavelength of 1550nm. The lattice constant of the photonic crystal structure was 517nm, the duty cycle was 0.32 (i.e., the width of the air medium in this embodiment was 165nm), the etching depth was 600nm, and the sidewall roughness was 5nm.

[0103] On the surface of the photonic crystal structure and the InP substrate, amorphous carbon films (i.e., the first conductive film and the second conductive film) with a thickness of 20 nm were deposited by magnetron sputtering. The root mean square roughness of the surface after depositing the amorphous carbon film in the non-etched region of CVD diamond and the root mean square roughness of the surface after depositing the amorphous carbon film on the InP surface are both 0.3 nm. The total thickness deviation between CVD diamond and InP substrate is 2 μm.

[0104] In a vacuum chamber with a vacuum level of 1E-6 Pa, the surfaces of a diamond substrate with a photonic crystal structure and an InP substrate were simultaneously activated using an argon fast atom beam. The activation time was 900 s at an argon atom beam energy of 1.5 keV, followed by room temperature vacuum bonding at a bonding pressure of 1.5 MPa for 1 minute. The InP substrate was then chemically etched using an H2SO4-H2O2 solution, followed by chemical mechanical polishing, to reduce the InP substrate to a thickness of 5 μm with a surface roughness of less than or equal to 0.5 nm.

[0105] This embodiment also provides a composite substrate structure obtained based on the above preparation method.

[0106] This invention uses a first substrate as a supporting substrate and integrates a photonic crystal structure on the supporting substrate to achieve multiple optical functions in the visible to infrared bands. It combines a first conductive film and a second conductive film as conductive non-metallic interlayers, thus balancing optical and electrical properties. The composite substrate structure of this invention is geared towards advanced packaging and heterogeneous integration applications. Compared with epitaxial monolithic integration, the bonding-based composite substrate structure offers greater flexibility in material selection and combination, and richer functionality.

[0107] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0108] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A composite substrate structure, characterized in that, include: The first substrate includes a first surface and a second surface disposed opposite to each other. A photonic crystal structure is formed on the first surface. The photonic crystal structure includes a plurality of photonic crystal units distributed at periodic intervals. A first conductive thin film is formed on the surface of the photonic crystal unit. The second substrate includes a third surface and a fourth surface disposed opposite to each other, wherein a second conductive thin film is formed on the third surface; The second substrate is located on the first substrate, and the second conductive film is bonded to the first conductive film.

2. The substrate structure according to claim 1, characterized in that, The first substrate is one of a diamond substrate, a SiC substrate, or a group V boride substrate; and / or, The first substrate is a single-crystal substrate or a polycrystalline substrate.

3. The substrate structure according to claim 1, characterized in that, The period of the photonic crystal structure is 100 nm to 5 μm, and the duty cycle is 0.05 to 0.95; and / or, The thickness of the photonic crystal unit is 10 nm to 10 μm; and / or, The side surface roughness of the photonic crystal unit is less than or equal to 5 nm.

4. The substrate structure according to claim 1, characterized in that, The second substrate is a III-V compound substrate; and / or, The thickness of the second substrate is 200 nm to 10 μm; and / or, The surface roughness of the fourth surface is less than or equal to 0.5 nm.

5. The substrate structure according to claim 1, characterized in that, The material of the first conductive film includes at least one of amorphous silicon, polycrystalline silicon, amorphous carbon, polycrystalline carbon, amorphous group III nitride, polycrystalline group III nitride, amorphous germanium, and polycrystalline germanium; and / or, The thickness of the first conductive film is 1 nm to 50 nm; and / or, The surface roughness of the first conductive film located on the upper surface of the photonic crystal unit is less than or equal to 0.5 nm.

6. The substrate structure according to claim 1, characterized in that, The material of the second conductive film includes at least one of amorphous silicon, polycrystalline silicon, amorphous carbon, polycrystalline carbon, amorphous group III nitride, polycrystalline group III nitride, amorphous germanium, and polycrystalline germanium; and / or, The thickness of the second conductive film is 1 nm to 50 nm; and / or, The surface roughness of the second conductive film is less than or equal to 0.5 nm.

7. A method for preparing a composite substrate structure, characterized in that, The preparation method includes: A first substrate is provided, the first substrate including a first surface and a second surface disposed opposite to each other; A photonic crystal structure is fabricated on the first surface by photolithography and / or etching, the photonic crystal structure comprising a plurality of periodically spaced photonic crystal units; A first conductive thin film is deposited on the surface of the photonic crystal structure; A second substrate is provided, the second substrate including a third surface and a fourth surface disposed opposite to each other; A second conductive thin film is deposited on the third surface of the second substrate; The second conductive film is bonded to the first conductive film.

8. The method for preparing the composite substrate structure according to claim 7, characterized in that, Before fabricating a photonic crystal structure on the first surface, the root mean square roughness of the first surface is reduced to less than or equal to 0.3 nm by chemical mechanical polishing and / or argon plasma surface treatment.

9. The method for preparing the composite substrate structure according to claim 7, characterized in that, Bonding the first conductive film to the second conductive film includes: In a vacuum environment, the photonic crystal structure of the first substrate and the third surface of the second substrate are simultaneously activated by an argon fast atom beam, wherein the energy of the argon fast atom beam is 0.5keV~2keV and the activation processing time is 100s~1000s. The first conductive film and the second conductive film are bonded in a vacuum environment at room temperature, with a bonding pressure of 0.5 MPa to 50 MPa and a bonding pressure duration of 1 to 10 minutes.

10. The method for preparing the composite substrate structure according to claim 7, characterized in that, After bonding the first conductive film to the second conductive film, the thickness of the second substrate is reduced to 200nm~10μm, and the surface roughness of the fourth surface of the second substrate is processed to be less than or equal to 0.5nm.

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