Optical waveguide composite film and preparation method thereof

Abstract

The invention belongs to the technical field of semiconductors, and particularly relates to an optical waveguide composite film and a preparation method thereof.The optical waveguide composite film comprises a substrate layer, an isolation layer, a waveguide composite body and a film layer which are stacked from bottom to top; wherein the waveguide complex comprises a silicon waveguide and a filling structure filled in the surrounding area of the silicon waveguide, the upper surface of the silicon waveguide and the upper surface of the filling structure are coplanar, and the silicon waveguide is seamlessly attached to the filling structure. According to the preparation method of the optical waveguide composite film, through surface treatment of polishing and ion beam etching, the upper surface of a silicon waveguide of a waveguide composite body is coplanar with the upper surface of a filling structure, the silicon waveguide is seamlessly attached to the filling structure, direct and stable bonding of the waveguide composite body and functional materials such as lithium niobate is achieved, the bonding strength is high, the film is not prone to falling off and breaking, and the service life of the film is prolonged. The yield is high.

Description

Technical Field

[0001] This application belongs to the field of semiconductor technology, specifically relating to an optical waveguide composite thin film and its preparation method. Background Technology

[0002] Currently, silicon is the most widely used semiconductor material in industrial applications and is extensively used in electronic components. However, silicon itself has a centrosymmetric crystal structure and lacks electro-optic effects, making it unsuitable for direct fabrication of high-performance electro-optic modulators and other electronic components. Therefore, it is usually necessary to rely on the plasma dispersion effect to realize the application of silicon materials in electro-optic modulators and other electronic components, but there is still a challenge in simultaneously achieving ultra-high speed and low half-wave voltage.

[0003] Lithium niobate and other crystals possess excellent nonlinear optical, electro-optic, and acousto-optic properties, making them widely applicable in optical signal processing and information storage. Therefore, some researchers have proposed integrating silicon materials with lithium niobate crystals, utilizing the light-guiding properties of silicon waveguides and the electro-optic modulation properties of lithium niobate for application in electro-optic modulators. By leveraging the advantages of lithium niobate crystals, the shortcomings of silicon materials can be effectively compensated for, improving the performance of electro-optic modulators and demonstrating promising application prospects.

[0004] Currently, the integration of silicon waveguides and lithium niobate crystals mainly involves bonding them using interlayer materials such as BCB (benzocyclobutene) or SiO2. However, as an additional layer, the thickness uniformity of the interlayer is difficult to control accurately, which may affect the modulation of the light field in lithium niobate, thus impacting the performance of the electro-optic modulator. Furthermore, bonding lithium niobate to silicon waveguides with BCB is prone to bubble formation, and the low operating temperature of BCB limits the temperature involved in the integration process, thereby restricting the effective integration of silicon waveguides and lithium niobate crystals. In addition, researchers attempted to directly bond lithium niobate to silicon waveguides. Specifically, the silicon waveguides were filled with heterogeneous filler materials, and then polished to achieve a smooth finish. However, the polishing removal rates of silicon and heterogeneous filler materials were inconsistent. After polishing, the material with the lower removal rate appeared as a protrusion, while the material with the higher removal rate appeared as a concave shape. Furthermore, gaps and pits also appeared at the interface between silicon and heterogeneous filler materials due to polishing. When bonding functional materials such as lithium niobate, the bonding strength was low and the materials were prone to detachment. Moreover, since functional materials such as lithium niobate ultimately exist in the form of micro- and nano-scale thin films, they are easily broken during the fabrication process. Summary of the Invention

[0005] Technical issues

[0006] The purpose of this invention is to provide an optical waveguide composite thin film and its preparation method, which solves the problems of difficulty in controlling the thickness and easy generation of bubbles when using an intermediate layer to bond silicon and lithium niobate during the integration process, and the appearance of convex / concave bonding surfaces when silicon and lithium niobate are directly bonded, resulting in gaps and pits at the contact interface between silicon material and heterogeneous filler material, leading to low bonding strength, easy detachment, and easy breakage of the film, thereby improving the yield and product yield.

[0007] Technical solution

[0008] The first aspect of this invention provides an optical waveguide composite thin film, comprising a substrate layer, an isolation layer, a waveguide composite, and a thin film layer stacked from bottom to top; wherein the waveguide composite includes a silicon waveguide and a filling structure filling the area surrounding the silicon waveguide, the upper surface of the silicon waveguide and the upper surface of the filling structure are coplanar, and the silicon waveguide and the filling structure are seamlessly bonded. In this invention, the upper surface of the silicon waveguide of the waveguide composite is coplanar with the upper surface of the filling structure, and the silicon waveguide and the filling structure are seamlessly bonded. That is, there are no pits or protrusions on the upper surface of the waveguide composite, and there are no gaps or pits at the contact interface between the silicon waveguide and the filling structure. The upper surface of the waveguide composite is in good condition, and the seamless contact between the silicon waveguide and the filling structure provides good bonding conditions, improves bonding strength, and allows functional materials such as lithium niobate to be directly and stably bonded to the silicon waveguide without easily detaching. Even if functional materials such as lithium niobate exist in the form of micro / nano-scale thin films, they are not easily broken, thus improving yield and productivity. At the same time, it avoids negative problems such as bubbles, limited temperature resistance, and low bonding strength that occur when bonding is done through an intermediate layer of materials such as BCB (benzocyclobutene) or SiO2.

[0009] In some embodiments, the silicon waveguide is a strip silicon waveguide with a thickness of 100 nm to 1 μm and a width of 200 nm to 1 μm.

[0010] In some embodiments, the number of silicon waveguides is one or more, and when the number of silicon waveguides is more than one, the silicon waveguides are arranged at intervals.

[0011] In some embodiments, the surface roughness Ra of the upper surface of the waveguide composite is ≤0.3 nm, which meets the surface roughness requirements of the bonding surface of the direct bonding pair.

[0012] In some embodiments, a trap layer is further provided between the substrate layer and the isolation layer, and the material of the trap layer is selected from polycrystalline silicon or amorphous silicon.

[0013] In some embodiments, the substrate layer is selected from one or more of lithium niobate, lithium tantalate, quartz, silicon, sapphire, silicon carbide, silicon nitride, gallium arsenide, or indium phosphide; the isolation layer is selected from one or more of silicon dioxide, silicon nitride, aluminum oxide, or aluminum nitride; the filling structure is selected from silicon dioxide or silicon nitride; and the thin film layer is selected from lithium niobate or lithium tantalate.

[0014] A second aspect of the present invention provides a method for preparing any of the above-mentioned optical waveguide composite thin films, comprising the following steps: preparing an optical waveguide composite substrate precursor, wherein the optical waveguide composite substrate precursor comprises a substrate layer, an isolation layer, and a waveguide composite precursor stacked from bottom to top, the waveguide composite precursor comprising a silicon waveguide precursor and a filler structure precursor; performing surface treatment on the upper surface of the waveguide composite precursor to obtain an optical waveguide composite substrate comprising a substrate layer, an isolation layer, and a waveguide composite stacked from bottom to top; bonding a thin film wafer on the upper surface of the optical waveguide composite substrate, and thinning the thin film wafer to obtain an optical waveguide composite thin film comprising a substrate layer, an isolation layer, a waveguide composite, and a thin film layer stacked from bottom to top; wherein the surface treatment comprises: sequentially performing polishing treatment and ion beam etching treatment on the upper surface of the waveguide composite precursor. The preparation method of this invention involves surface treatment of the upper surface of the waveguide composite precursor through polishing and ion beam etching. This ensures that the upper surface of the waveguide composite is free of pits and protrusions, and that there are no gaps or pits at the interface between the silicon waveguide and the filling structure. The upper surface of the waveguide composite is in good condition, and the silicon waveguide and the filling structure assembly are in seamless contact, providing excellent bonding conditions. This enables direct and stable bonding of the waveguide composite with functional materials such as lithium niobate, resulting in high bonding strength, thin film that is not easily detached or broken, and high yield and high production rate.

[0015] In some embodiments, the optical waveguide composite substrate precursor is prepared by the following steps: preparing a substrate layer and preparing an isolation layer on the substrate layer; spraying photoresist onto the upper surface of the isolation layer, setting a photomask on the photoresist to form a light-transmitting area identical to the waveguide pattern, exposing and modifying the photoresist through the light-transmitting area, forming a modified area on the photoresist at a position corresponding to the light-transmitting area, removing the modified area to obtain a photoresist with openings, the shape of which is identical to the waveguide pattern; depositing silicon material on the photoresist with openings, removing the photoresist to obtain a silicon waveguide precursor located on the isolation layer; depositing a filling structure precursor on the isolation layer and the silicon waveguide precursor to obtain the optical waveguide composite substrate precursor.

[0016] In some embodiments, the method of preparing the isolation layer is not limited. For example, the isolation layer can be prepared by deposition or thermal oxidation.

[0017] In some embodiments, before fabricating the isolation layer, a trap layer is first fabricated on the substrate layer, and then an isolation layer is fabricated on the trap layer.

[0018] In some embodiments, the method of preparing the trap layer is not limited; for example, the trap layer can be prepared by deposition.

[0019] In some embodiments, the deposition method is chemical vapor deposition (CVD) or physical vapor deposition (PVD).

[0020] In some embodiments, the modified area is removed by rinsing with a developer.

[0021] In some embodiments, the method of removing the photoresist is not limited. For example, the photoresist can be removed by dissolving it with a chemical solvent. The chemical solvent can be a chemical solvent containing components such as propylene glycol methyl ether acetate, N-methylpyrrolidone, or dimethyl sulfoxide, or a commercially available special photoresist thinner / cleaning solution.

[0022] In some embodiments, the specific process of the surface treatment is as follows: The upper surface of the waveguide composite precursor is polished to remove the deposited filler structure precursor on the silicon waveguide precursor, exposing the silicon waveguide precursor; surface morphology data of the upper surface of the waveguide composite precursor after polishing is obtained; based on the surface morphology data, gap / pit data at the interface between the silicon waveguide precursor and the filler structure precursor is obtained; based on the gap / pit data, the lowest point of the gap / pit is obtained; based on the lowest point of the gap / pit, an etching reference surface is obtained; based on the surface morphology data and the etching reference surface, the etching depth at different positions on the upper surface of the waveguide composite precursor is determined; based on the etching depth at different positions on the upper surface of the waveguide composite precursor, the upper surface of the polished waveguide composite precursor is subjected to ion beam etching to obtain the optical waveguide composite substrate. In the fabrication process of this invention, the upper surface of the waveguide composite precursor is surface-treated. First, polishing is performed to remove the deposited filler structure precursor on the silicon waveguide precursor, exposing it. Then, based on the surface morphology data of the upper surface of the waveguide composite precursor after polishing, the gap and pit data at the interface between the silicon waveguide precursor and the filler structure precursor are obtained, and the lowest point of the gap and pit is determined. Based on the lowest point of the gap and pit, an etching reference surface is obtained, thereby determining the etching depth at different positions on the upper surface of the waveguide composite precursor. Based on the etching depth at different positions on the waveguide composite precursor, the upper surface of the polished waveguide composite precursor is subjected to ion beam etching to eliminate the defects caused by polishing. The uneven polishing removal rates of silicon and heterogeneous filler materials introduce protrusions and gaps / pits at the interface between them, resulting in an optical waveguide composite substrate. The upper surface of this substrate, corresponding to the upper surface of the waveguide composite, is free of pits, protrusions, and gaps / pits at the interface between the silicon waveguide and the filler structure. This results in a superior surface condition, seamless contact between the silicon waveguide and the filler structure, providing excellent bonding conditions and increased bonding strength. Direct bonding with functional materials such as lithium niobate is possible, preventing detachment of these materials. Even when these materials exist in micro / nanoscale thin films, they remain relatively intact, improving yield and productivity. Furthermore, this avoids the negative issues associated with bonding via intermediate layers such as BCB (benzocyclobutene) or SiO2.

[0023] In some embodiments, the method of obtaining the surface morphology data of the upper surface of the waveguide composite precursor after polishing is not limited. For example, the surface morphology data of the upper surface of the waveguide composite precursor after polishing can be obtained by atomic force microscopy (AFM). The surface morphology data includes the morphology of the upper surface of the waveguide composite precursor after polishing, from which gap and pit data at the contact interface between the silicon waveguide precursor and the filling structure precursor can be read, and the lowest point of the gap and pit can be read from the gap and pit data.

[0024] In some embodiments, the etching reference surface is a horizontal plane passing through the lowest point of the slot pit; the etching depth at different positions on the upper surface of the waveguide composite precursor is obtained by: obtaining the height data at different positions on the upper surface of the waveguide composite precursor based on the surface topography data; the distance from the height data to the etching reference surface is recorded as the etching depth at different positions on the upper surface of the waveguide composite precursor, in other words, the height data at different positions on the upper surface of the waveguide composite precursor minus the height data of the etching reference surface is recorded as the etching depth at different positions on the upper surface of the waveguide composite precursor.

[0025] In some embodiments, the specific process parameters for ion beam etching are not limited, as long as the required amount of etching can be removed at different locations on the upper surface of the waveguide composite precursor. In this embodiment, to simplify the process, fixed etching parameters are preferred, and the etching amount at different locations on the upper surface of the waveguide composite precursor is controlled by only changing the etching time at those locations. Alternatively, the ion energy or beam current density at locations with higher etching amounts can be increased to simultaneously complete the etching at different locations on the upper surface of the waveguide composite precursor within the same etching time.

[0026] In some embodiments, a thin film wafer is bonded to the upper surface of the optical waveguide composite substrate. The specific process of thinning the thin film wafer is as follows: a thin film wafer precursor is prepared, and ion implantation is performed on the thin film wafer precursor to obtain a thin film wafer. The thin film wafer includes a thin film layer, a residual layer, and a separation layer located between the thin film layer and the residual layer. The implanted ions are concentrated in the separation layer. The optical waveguide composite substrate and the thin film wafer are bonded through the upper surface of the optical waveguide composite substrate and the thin film layer side of the thin film wafer to obtain a bonded body. The bonded body is annealed, the thin film wafer is peeled off from the separation layer, the thin film layer remains on the waveguide composite body, and the exposed surface of the thin film layer is polished to remove the separation layer residue, thereby obtaining an optical waveguide composite thin film comprising a substrate layer, an isolation layer, a waveguide composite body, and a thin film layer stacked from bottom to top.

[0027] In some embodiments, the implanted ions, ion implantation dose, and ion implantation energy are not particularly limited and can be reasonably adjusted as needed. For example, the implanted ions may be one or more of hydrogen ions, helium ions, nitrogen ions, oxygen ions, or argon ions; the ion implantation dose may be 1 × 10⁻⁶. 16 ~3×10 17 ions / cm 2 The ion implantation energy is 30 keV to 5 MeV.

[0028] In some embodiments, before bonding the optical waveguide composite substrate and the thin film wafer, the upper surface of the optical waveguide composite substrate and the thin film layer side of the thin film wafer are cleaned.

[0029] In some embodiments, the upper surface of the cleaned optical waveguide composite substrate and / or the side surface of the thin film layer of the thin film wafer are activated, and then bonded.

[0030] In some embodiments, the activation method is plasma activation or chemical solution activation.

[0031] In some embodiments, the process parameters of the annealing treatment are not particularly limited and can be freely selected according to requirements. For example, the annealing temperature of the annealing treatment is 100~600℃ and the annealing time is 1~24 h. Attached Figure Description

[0032] Figure 1 The optical waveguide composite thin film prepared in Example 1; Figure 2 This is a flowchart illustrating the preparation of a lithium niobate optical waveguide composite thin film in Example 1; Figure 3 This is an atomic force microscope (AFM) cross-sectional analysis image of the upper surface of the waveguide composite precursor after polishing in Example 1. Figure 4 This is a surface roughness diagram of the upper surface of the waveguide composite in Example 1; Figure 5 This is an atomic force microscope (AFM) cross-sectional analysis image of the upper surface of the waveguide composite in Example 1. Figure 6 The optical waveguide composite thin film prepared in Example 2; Figure 7 This is a flowchart illustrating the preparation of a lithium niobate optical waveguide composite thin film in Example 2. Detailed Implementation

[0033] To facilitate the implementation of the technical solution applied for, the following is a general explanation and definition of the terms and expressions used in this application.

[0034] The terms “comprising,” “including,” or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase “comprising one…” does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0035] In the comparative experiments provided in this application, unless otherwise specified, all other experimental conditions and materials are kept consistent to ensure comparability.

[0036] Unless otherwise specified, all reagents and instruments used in the embodiments of this invention can be purchased from the market.

[0037] The claims of this invention do not specifically limit the order of steps, and those skilled in the art can make reasonable adjustments to the order of steps during actual implementation.

[0038] The following provides a further description of an optical waveguide composite thin film and its preparation method provided in this application.

[0039] Example 1: Lithium niobate optical waveguide composite thin film and its preparation This embodiment provides an optical waveguide composite thin film, such as Figure 1 As shown, the structure includes a silicon substrate layer, a silicon dioxide isolation layer, a waveguide composite, and a lithium niobate thin film layer stacked from bottom to top. The waveguide composite includes a strip-shaped silicon waveguide and a silicon dioxide filling structure surrounding the strip-shaped silicon waveguide. The upper surface of the strip-shaped silicon waveguide is coplanar with the upper surface of the silicon dioxide filling structure, and the strip-shaped silicon waveguide and the silicon dioxide filling structure are seamlessly bonded at their interface.

[0040] In this embodiment, the surface roughness Ra of the upper surface of the waveguide composite is ≤0.3 nm.

[0041] In this embodiment, the thickness of the strip silicon waveguide is 100 nm and the width is 200 nm. There are multiple strip silicon waveguides, which are arranged at intervals.

[0042] This embodiment also provides a method for preparing the optical waveguide composite thin film of this embodiment, such as... Figure 2 As shown, it includes the following steps: S1. Prepare an optical waveguide composite substrate precursor, wherein the optical waveguide composite substrate precursor includes a silicon substrate layer, a silicon dioxide isolation layer and a waveguide composite precursor stacked from bottom to top, and the waveguide composite precursor includes multiple strip silicon waveguide precursors and silicon dioxide filled structure precursors.

[0043] Specifically, the optical waveguide composite substrate precursor is prepared through the following steps: A silicon substrate layer is prepared, and a silicon dioxide isolation layer is prepared on the silicon substrate layer by thermal oxidation; photoresist is sprayed onto the surface of the silicon dioxide isolation layer, and a photomask is set on the photoresist to form a light-transmitting area identical to the strip-shaped silicon waveguide pattern; the photoresist is exposed and modified through the light-transmitting area, forming a modified area on the photoresist at the position corresponding to the light-transmitting area; the modified area is removed by rinsing with a developer to obtain a photoresist with openings, the shape of which is the same as the strip-shaped silicon waveguide pattern; silicon material is deposited on the photoresist with openings to remove… Remove the photoresist (the method of photoresist removal is not limited, for example, it can be dissolved by chemical solvents, such as those containing propylene glycol methyl ether acetate, N-methylpyrrolidone or dimethyl sulfoxide, or commercially available photoresist thinners / cleaning solutions), to obtain a strip-shaped silicon waveguide precursor on a silicon dioxide isolation layer; deposit a silicon dioxide filling structure precursor on the silicon dioxide isolation layer and the strip-shaped silicon waveguide precursor. When the silicon dioxide filling structure precursor fills the area around the strip-shaped silicon waveguide precursor, it will be deposited on the strip-shaped silicon waveguide precursor at the same time, to obtain an optical waveguide composite substrate precursor.

[0044] S2. Perform surface treatment on the upper surface of the waveguide composite precursor to obtain an optical waveguide composite substrate comprising a silicon substrate layer, a silicon dioxide isolation layer, and a waveguide composite layer stacked from bottom to top.

[0045] Specifically, the surface treatment process is as follows: the upper surface of the waveguide composite precursor is polished to remove the silica-filled precursor deposited on the strip-shaped silicon waveguide precursor, exposing the strip-shaped silicon waveguide precursor; surface morphology data of the upper surface of the waveguide composite precursor after polishing is obtained by atomic force microscopy (AFM), such as... Figure 3 The figure shows an atomic force microscope (AFM) cross-sectional analysis of the upper surface of the waveguide composite precursor after polishing. As can be seen from the figure, the surface morphology data includes the morphology of the upper surface of the waveguide composite precursor after polishing. Based on this surface morphology data, the gap and pit data at the contact interface between the strip silicon waveguide precursor and the silica-filled structure precursor can be read. The lowest point of the gap and pit can be read from the gap and pit data, such as... Figure 3As shown, the lowest point of the slit pit is around -7 nm, meaning the slit pit depth at the interface between the strip silicon waveguide precursor and the silicon dioxide-filled structure precursor is approximately 7 nm. Based on the lowest point of the slit pit, the horizontal plane passing through the lowest point of the slit pit is designated as the etching reference plane. Based on the surface morphology data and the etching reference plane, height data at different positions on the upper surface of the waveguide composite precursor are read from the surface morphology data. The distance from the height data to the etching reference plane is designated as the etching depth at different positions on the upper surface of the waveguide composite precursor. In other words, the height data at different positions on the upper surface of the waveguide composite precursor minus the height data of the etching reference plane is designated as the etching depth at different positions on the upper surface of the waveguide composite precursor. Based on the etching depth at different positions on the waveguide composite precursor, the upper surface of the polished waveguide composite precursor is subjected to ion beam etching to obtain the optical waveguide composite substrate. In this embodiment, the specific process parameters for ion beam etching are not limited, as long as the required amount of etching can be removed at different positions on the upper surface of the waveguide composite precursor. To simplify the process, fixed etching parameters are preferred, controlling the etching amount at different positions on the upper surface of the waveguide composite precursor by only changing the etching time. Alternatively, the ion energy or beam current density at positions with higher etching amounts can be increased to simultaneously complete etching at different positions on the upper surface of the waveguide composite precursor within the same etching time. In this embodiment, after ion beam etching of the polished upper surface of the waveguide composite precursor, preferably, the upper surface is slightly polished. This polishing time is short and will not degrade the upper surface, resulting in an optical waveguide composite substrate. Figure 4 and 5 As shown, after ion beam etching, the surface roughness Ra of the upper surface of the waveguide composite is 0.272 nm. The protrusion height of the silica-filled structure or the depth of the gap pit at the contact interface in the region surrounding the strip silicon waveguide are 0.7 nm and 0.9 nm, respectively. The surface roughness, protrusion height, and depth of the gap pit at the contact interface are extremely small and can be ignored. The upper surface of the strip silicon waveguide and the upper surface of the silica-filled structure are coplanar and level, and the strip silicon waveguide and the silica-filled structure are seamlessly bonded at their contact interface, which has no effect on direct bonding.

[0046] S3. A lithium niobate thin film wafer is bonded to the upper surface of the optical waveguide composite substrate (i.e., the upper surface of the waveguide composite), and the lithium niobate thin film wafer is thinned to obtain an optical waveguide composite film comprising a silicon substrate layer, a silicon dioxide isolation layer, a waveguide composite and a lithium niobate thin film layer stacked from bottom to top.

[0047] Specifically, a lithium niobate thin film wafer precursor is prepared. Ion implantation is performed on the lithium niobate thin film wafer precursor from its bonding surface to obtain a lithium niobate thin film wafer. The lithium niobate thin film wafer includes a thin film layer near the bonding surface, a residual layer away from the bonding surface, and a separation layer located between the thin film layer and the residual layer. The implanted ions are concentrated in the separation layer. In this embodiment, the implanted ions, ion implantation dose, and ion implantation energy are not particularly limited and can be reasonably adjusted as needed. For example, the implanted ions can be one or more of hydrogen ions, helium ions, nitrogen ions, oxygen ions, or argon ions; the ion implantation dose is 1×10⁻⁶. 16 ~3×10 17 ions / cm 2 The ion implantation energy is 30 keV to 5 MeV. In this embodiment, the implanted ions are helium ions, and the ion implantation dose is 5 × 10⁻⁶. 16 ions / cm 2 The ion implantation energy is 500 keV.

[0048] The optical waveguide composite substrate and the lithium niobate thin film wafer are bonded together via the upper surface of the optical waveguide composite substrate and the thin film layer side (bonding surface) of the lithium niobate thin film wafer to form a bond. In this embodiment, preferably, before bonding the optical waveguide composite substrate and the lithium niobate thin film wafer, the upper surface of the optical waveguide composite substrate and the thin film layer side (bonding surface) of the lithium niobate thin film wafer are cleaned, and the cleaned upper surface of the optical waveguide composite substrate and / or the thin film layer side (bonding surface) of the lithium niobate thin film wafer are subjected to plasma activation treatment before bonding.

[0049] The bonding composite is annealed, and the lithium niobate thin film wafer is peeled off from the separation layer, leaving the thin film layer on the waveguide composite. The upper surface (exposed surface) of the thin film layer is polished to remove the separation layer residue, resulting in an optical waveguide composite thin film comprising a silicon substrate layer, a silicon dioxide isolation layer, a waveguide composite, and a lithium niobate thin film layer stacked from bottom to top. In this embodiment, the annealing process parameters are not particularly limited and can be freely selected according to requirements. For example, the annealing temperature is 100~600℃ and the annealing time is 1~24 h. In this embodiment, the annealing temperature is selected as 200℃ and the annealing time is 20 h.

[0050] Example 2: Lithium niobate optical waveguide composite thin film and its preparation This embodiment provides an optical waveguide composite thin film, such as Figure 6As shown, the structure includes, from bottom to top, a silicon substrate layer, a polycrystalline silicon trap layer, a silicon nitride isolation layer, a waveguide composite, and a lithium niobate thin film layer. The waveguide composite comprises a strip-shaped silicon waveguide and a silicon nitride filling structure surrounding the strip-shaped silicon waveguide. The upper surface of the strip-shaped silicon waveguide is coplanar with the upper surface of the silicon nitride filling structure, and the strip-shaped silicon waveguide and the silicon nitride filling structure are seamlessly bonded at their interface.

[0051] In this embodiment, the surface roughness Ra of the upper surface of the waveguide composite is ≤0.3 nm.

[0052] In this embodiment, the thickness of the strip silicon waveguide is 500 nm and the width is 500 nm. There are multiple strip silicon waveguides, which are arranged at intervals.

[0053] This embodiment also provides a method for preparing the optical waveguide composite thin film of this embodiment, such as... Figure 7 As shown, it includes the following steps: S1. Prepare an optical waveguide composite substrate precursor, wherein the optical waveguide composite substrate precursor includes a silicon substrate layer, a polycrystalline silicon trap layer, a silicon nitride isolation layer and a waveguide composite precursor stacked from bottom to top, and the waveguide composite precursor includes multiple strip silicon waveguide precursors and silicon nitride filled structure precursors.

[0054] Specifically, the optical waveguide composite substrate precursor is prepared through the following steps: A silicon substrate layer is prepared; a polycrystalline silicon trap layer is deposited on the silicon substrate layer; a silicon nitride isolation layer is then deposited on the polycrystalline silicon trap layer; photoresist is sprayed onto the surface of the silicon nitride isolation layer; a photomask is placed on the photoresist to form a light-transmitting area identical to the strip-shaped silicon waveguide pattern; the photoresist is exposed and modified through the light-transmitting area, forming a modified area on the photoresist at the position corresponding to the light-transmitting area; the modified area is removed by rinsing with a developer to obtain a photoresist with openings, the shape of which is the same as the strip-shaped silicon waveguide pattern; the photoresist with openings... Silicon material is deposited on the photoresist of the hole, and the photoresist is removed (the method of photoresist removal is not limited, for example, chemical solvents can be used to dissolve it, such as chemical solvents containing propylene glycol methyl ether acetate, N-methylpyrrolidone or dimethyl sulfoxide, or commercially available special photoresist thinners / cleaning solutions), to obtain a strip-shaped silicon waveguide precursor located on the silicon nitride isolation layer; a silicon nitride filling structure precursor is deposited on the silicon nitride isolation layer and the strip-shaped silicon waveguide precursor. When the silicon nitride filling structure precursor fills the area around the strip-shaped silicon waveguide precursor, it will be deposited on the strip-shaped silicon waveguide precursor at the same time, to obtain the optical waveguide composite substrate precursor.

[0055] S2. Perform surface treatment on the upper surface of the waveguide composite precursor to obtain an optical waveguide composite substrate comprising a silicon substrate layer, a polysilicon trap layer, a silicon nitride isolation layer, and a waveguide composite layer stacked from bottom to top.

[0056] Specifically, the surface treatment process is as follows: The upper surface of the waveguide composite precursor is polished to remove the silicon nitride-filled structure precursor deposited on the strip silicon waveguide precursor, exposing the strip silicon waveguide precursor. Surface morphology data of the upper surface of the waveguide composite precursor after polishing is obtained using atomic force microscopy (AFM). This surface morphology data includes the morphology of the upper surface of the waveguide composite precursor after polishing. Based on this surface morphology data, gap and pit data at the contact interface between the strip silicon waveguide precursor and the silicon nitride-filled structure precursor can be read. The lowest point of the gap and pit (corresponding to the depth of the gap and pit) can be read from the gap and pit data. Based on the lowest point of the gap and pit… The horizontal plane passing through the lowest point of the slit pit is designated as the etching reference plane. Based on the surface topography data and the etching reference plane, the height data at different positions on the upper surface of the waveguide composite precursor is read from the surface topography data. The distance from the height data to the etching reference plane is designated as the etching depth at different positions on the upper surface of the waveguide composite precursor. In other words, the height data at different positions on the upper surface of the waveguide composite precursor minus the height data of the etching reference plane is designated as the etching depth at different positions on the upper surface of the waveguide composite precursor. Based on the etching depth at different positions on the waveguide composite precursor, the upper surface of the polished waveguide composite precursor is subjected to ion beam etching to obtain the optical waveguide composite substrate. In this embodiment, the specific process parameters for ion beam etching are not limited, as long as the required amount of etching can be removed at different positions on the upper surface of the waveguide composite precursor according to the etching depth. In this embodiment, to simplify the process, fixed etching parameters are preferred, and the etching amount at different positions on the upper surface of the waveguide composite precursor is controlled by only changing the etching time at different positions on the upper surface of the waveguide composite precursor; alternatively, the ion energy or beam current density at positions with large etching amounts can be increased to simultaneously complete the etching at different positions on the upper surface of the waveguide composite precursor within the same etching time. In this embodiment, after ion beam etching of the upper surface of the polished waveguide composite precursor, it is preferred to slightly polish the upper surface. This polishing time is short and will not degrade the upper surface, resulting in an optical waveguide composite substrate.

[0057] S3. A lithium niobate thin film wafer is bonded to the upper surface of the optical waveguide composite substrate (i.e., the upper surface of the waveguide composite), and the lithium niobate thin film wafer is thinned to obtain an optical waveguide composite film comprising a silicon substrate layer, a polycrystalline silicon trap layer, a silicon nitride isolation layer, a waveguide composite, and a lithium niobate thin film layer stacked from bottom to top.

[0058] Specifically, a lithium niobate thin film wafer precursor is prepared. Ion implantation is performed on the lithium niobate thin film wafer precursor from its bonding surface to obtain a lithium niobate thin film wafer. The lithium niobate thin film wafer includes a thin film layer near the bonding surface, a residual layer away from the bonding surface, and a separation layer located between the thin film layer and the residual layer. The implanted ions are concentrated in the separation layer. In this embodiment, the implanted ions, ion implantation dose, and ion implantation energy are not particularly limited and can be reasonably adjusted as needed. For example, the implanted ions can be one or more of hydrogen ions, helium ions, nitrogen ions, oxygen ions, or argon ions; the ion implantation dose is 1×10⁻⁶. 16 ~3×10 17 ions / cm 2 The ion implantation energy is 30 keV to 5 MeV. In this embodiment, the implanted ion is a hydrogen ion, and the ion implantation dose is 1 × 10⁻⁶. 17 ions / cm 2 The ion implantation energy is 300 keV.

[0059] The optical waveguide composite substrate and the lithium niobate thin film wafer are bonded together via the upper surface of the optical waveguide composite substrate and the thin film layer side (bonding surface) of the lithium niobate thin film wafer to form a bond. In this embodiment, preferably, before bonding the optical waveguide composite substrate and the lithium niobate thin film wafer, the upper surface of the optical waveguide composite substrate and the thin film layer side (bonding surface) of the lithium niobate thin film wafer are cleaned, and the cleaned upper surface of the optical waveguide composite substrate and / or the thin film layer side (bonding surface) of the lithium niobate thin film wafer are subjected to plasma activation treatment before bonding.

[0060] The bonding composite is annealed, and the lithium niobate thin film wafer is peeled off from the separation layer, leaving the thin film layer on the waveguide composite. The upper surface (exposed surface) of the thin film layer is polished to remove the separation layer residue, resulting in an optical waveguide composite film comprising a silicon substrate layer, a polycrystalline silicon trap layer, a silicon nitride isolation layer, a waveguide composite, and a lithium niobate thin film layer stacked from bottom to top. In this embodiment, the annealing process parameters are not particularly limited and can be freely selected according to requirements. For example, the annealing temperature is 100~600℃ and the annealing time is 1~24 h. In this embodiment, the annealing temperature is selected as 400℃ and the annealing time is 10 h.

[0061] Example 3: Lithium niobate optical waveguide composite thin film and its preparation This embodiment provides an optical waveguide composite thin film and its preparation method. It differs from Embodiment 1 only in the number, thickness, and width of the strip silicon waveguides; the rest are the same. The identical parts will not be described again here; only the differences will be explained as follows: In this embodiment, there is one strip silicon waveguide with a thickness of 300 nm and a width of 600 nm.

[0062] Example 4: Lithium niobate optical waveguide composite thin film and its preparation This embodiment provides an optical waveguide composite thin film and its preparation method. The only difference from Embodiment 1 is the substrate material; the rest are the same. The identical parts will not be described again here; only the differences will be explained, as follows: In this embodiment, the substrate material is silicon carbide.

[0063] Example 5: Lithium niobate optical waveguide composite thin film and its preparation This embodiment provides an optical waveguide composite thin film and its preparation method. The only difference from Embodiment 2 is the material of the insulating layer and the filling structure; the rest are the same. The identical parts will not be described again here; only the differences will be explained as follows: In this embodiment, the isolation layer is made of silicon dioxide, and the filling structure is also made of silicon dioxide.

[0064] Example 6: Lithium tantalate optical waveguide composite thin film and its preparation This embodiment provides an optical waveguide composite thin film and its preparation method. The only difference from Embodiment 1 is the material of the thin film wafer and the thin film layer; the rest are the same. The identical parts will not be described again here; only the differences will be explained as follows: In this embodiment, the thin film wafer is made of lithium tantalate, and the resulting thin film layer is also made of lithium tantalate.

[0065] Example 7: Lithium tantalate optical waveguide composite thin film and its preparation This embodiment provides an optical waveguide composite thin film and its preparation method. The only difference between this embodiment and Embodiment 2 is the material of the thin film wafer and the thin film layer. The rest are the same. The same parts will not be described again here. Only the different parts will be described as follows: The material of the thin film wafer in this embodiment is lithium tantalate, and the material of the thin film layer obtained therefrom is lithium tantalate.

[0066] The above specific embodiments further illustrate the purpose, technical solution and beneficial effects of this application. It should be understood that the above are only specific embodiments of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made on the basis of the technical solution of this application should be included within the scope of protection of this application.

Claims

1. An optical waveguide composite thin film, characterized in that, It includes a substrate layer, an isolation layer, a waveguide composite, and a thin film layer stacked from bottom to top; The waveguide composite includes a silicon waveguide and a filling structure that fills the area surrounding the silicon waveguide. The upper surface of the silicon waveguide is coplanar with the upper surface of the filling structure, and the silicon waveguide and the filling structure are seamlessly bonded together.

2. The optical waveguide composite thin film according to claim 1, characterized in that, The silicon waveguide is a strip-shaped silicon waveguide with a thickness of 100 nm to 1 μm and a width of 200 nm to 1 μm.

3. The optical waveguide composite thin film according to claim 1, characterized in that, The number of silicon waveguides is one or more. When the number of silicon waveguides is more than one, the silicon waveguides are arranged at intervals.

4. The optical waveguide composite thin film according to claim 1, characterized in that, The surface roughness Ra of the upper surface of the waveguide composite is ≤0.3 nm.

5. The optical waveguide composite thin film according to claim 1, characterized in that, A trap layer is provided between the substrate layer and the isolation layer, and the material of the trap layer is selected from polycrystalline silicon or amorphous silicon.

6. The optical waveguide composite thin film according to claim 1, characterized in that, The substrate layer is made of one or more of lithium niobate, lithium tantalate, quartz, silicon, sapphire, silicon carbide, silicon nitride, gallium arsenide, or indium phosphide; the isolation layer is made of one or more of silicon dioxide, silicon nitride, aluminum oxide, or aluminum nitride; the filling structure is made of silicon dioxide or silicon nitride; and the thin film layer is made of lithium niobate or lithium tantalate.

7. The method for preparing the optical waveguide composite thin film according to any one of claims 1-6, characterized in that, Includes the following steps: Prepare an optical waveguide composite substrate precursor, the optical waveguide composite substrate precursor comprising a substrate layer, an isolation layer and a waveguide composite precursor stacked from bottom to top, the waveguide composite precursor comprising a silicon waveguide precursor and a filler structure precursor; The upper surface of the waveguide composite precursor is surface treated to obtain an optical waveguide composite substrate comprising a substrate layer, an isolation layer and a waveguide composite stacked from bottom to top. A thin film wafer is bonded to the upper surface of the optical waveguide composite substrate, and the thin film wafer is thinned to obtain an optical waveguide composite film comprising a substrate layer, an isolation layer, a waveguide composite and a thin film layer stacked from bottom to top. The surface treatment includes: sequentially polishing and ion beam etching the upper surface of the waveguide composite precursor.

8. The preparation method according to claim 7, characterized in that, The optical waveguide composite substrate precursor is prepared through the following steps: Prepare a substrate layer, and fabricate an isolation layer on the substrate layer; Photoresist is sprayed onto the upper surface of the isolation layer, and a photomask is set on the photoresist to form a light-transmitting area that is the same as the waveguide pattern. The photoresist is exposed and modified through the light-transmitting area, and a modified area is formed at the position of the photoresist corresponding to the light-transmitting area. The modified area is removed to obtain a photoresist with an opening, the shape of which is the same as the waveguide pattern. Silicon material is deposited on photoresist with openings, and the photoresist is removed to obtain a silicon waveguide precursor located on an isolation layer. A filler structure precursor is deposited on the isolation layer and the silicon waveguide precursor to obtain the optical waveguide composite substrate precursor.

9. The preparation method according to claim 8, characterized in that, Before fabricating the isolation layer, a trap layer is first fabricated on the substrate layer, and then an isolation layer is fabricated on the trap layer.

10. The preparation method according to claim 7, characterized in that, The specific process of the surface treatment is as follows: The upper surface of the waveguide composite precursor is polished to remove the filled structure precursor deposited on the silicon waveguide precursor, exposing the silicon waveguide precursor. Surface morphology data of the upper surface of the waveguide composite precursor after polishing is obtained. Based on the surface morphology data, gap and pit data at the contact interface between the silicon waveguide precursor and the filling structure precursor are obtained. Based on the gap and pit data, the lowest point of the gap and pit is obtained. Based on the lowest point of the groove pit, the etching reference surface is obtained; Based on the surface topography data and the etching reference surface, the etching depth at different locations on the upper surface of the waveguide composite precursor is determined. Based on the etching depth at different positions on the upper surface of the waveguide composite precursor, the upper surface of the polished waveguide composite precursor is subjected to ion beam etching to obtain the optical waveguide composite substrate.

11. The preparation method according to claim 10, characterized in that, The etching reference surface is a horizontal plane passing through the lowest point of the slit pit; The etching depth at different locations on the upper surface of the waveguide composite precursor is obtained by the following method: based on the surface topography data, the height data at different locations on the upper surface of the waveguide composite precursor is obtained; the distance from the height data to the etching reference surface is the etching depth at different locations on the upper surface of the waveguide composite precursor.

12. The preparation method according to claim 7, characterized in that, The specific process of bonding a thin film wafer to the upper surface of the optical waveguide composite substrate and thinning the thin film wafer is as follows: Prepare a thin film wafer precursor, perform ion implantation on the thin film wafer precursor to obtain a thin film wafer, the thin film wafer including a thin film layer, a residual layer and a separation layer located between the thin film layer and the residual layer, the implanted ions are concentrated in the separation layer. The optical waveguide composite substrate and the thin film wafer are bonded together by bonding the optical waveguide composite substrate and the thin film layer side of the thin film wafer to obtain a bonded body; The bonding body is annealed, the thin film wafer is peeled off from the separation layer, the thin film layer is retained on the waveguide composite, and the exposed surface of the thin film layer is polished to obtain an optical waveguide composite thin film comprising a substrate layer, an isolation layer, a waveguide composite and a thin film layer stacked from bottom to top.

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