Thin film structures based on integrated optics and methods of forming same

Abstract

Thin film structures based on integrated optics and methods of forming the same are disclosed. A method for forming a thin film structure based on integrated optics comprises the steps of: providing a polishing solution comprising a mesoporous polishing abrasive; providing a sample comprising a substrate, a thin film layer on the substrate, and a hard mask layer on the thin film layer wherein at least a portion of the thin film layer is exposed; etching the thin film layer to remove at least one part of the exposed part of the thin film layer; chemically and mechanically polishing the etched exposed part of the thin film layer by using a polishing solution comprising a mesoporous polishing abrasive; and removing the hard mask layer.

Description

Technical Field

[0001] This application relates to the fabrication of thin films based on integrated optical devices, and more particularly to their planarization process. Background Technology

[0002] Integrated optical devices have various thin-film structures.

[0003] For example, lithium niobate crystals possess high nonlinear optical coefficients, photoelectric effects, piezoelectric effects, photorefractive effects, photovoltaic effects, and acousto-optic effects, making them ideal substrate materials for photonic integration. Lithium niobate thin films (TFLNs) not only integrate the advantages of lithium niobate crystals but also possess advantages such as high optical field confinement and high integration, earning them the title of "optical silicon." In silicon heterogeneous integrated photonic chips, TFLNs can be applied in various ways, such as electro-optic modulators, optical waveguides, optical frequency combs, microrings, and microcavity disks.

[0004] TFLN optical waveguides are optical waveguide devices based on TFLN material. Their operation is based on the interaction between the electro-optic effect and optical waveguide modes. They are mainly used for optical signal transmission and control in integrated photonic circuits and optical communication systems. TFLN optical waveguides possess advantages such as strong electro-optic effect, excellent nonlinear optical properties, wide optical frequency range, and high integration capability with optoelectronic devices.

[0005] The fabrication of TFLN optical waveguides primarily relies on electron beam lithography (EBL) patterning combined with inductively coupled plasma (ICP) and reactive ion etching (RIE) to create ridge waveguides. This fabrication method results in high sidewall roughness in the ridge waveguides, causing light scattering at the sidewalls and extending part of the optical field distribution beyond the waveguide, thus leading to transmission loss. To reduce waveguide transmission loss, traditionally, electron beam or ultraviolet lithography combined with ion beam etching techniques are used, but these techniques are difficult to fabricate and result in high losses. Furthermore, during the fabrication of TFLN optical waveguides on insulators, the sidewalls of the etched ridge waveguides are often not flat enough, leading to increased light scattering losses. Therefore, etching combined with chemical mechanical polishing (CMP) is often used to reduce sidewall roughness.

[0006] Chemical Mechanical Polishing (CMP) is hailed as the only technology currently available capable of achieving global surface planarization of wafers in integrated circuit manufacturing. It can achieve atomic-level ultra-high flatness, directly impacting the final chip quality and yield. CMP technology utilizes the synergistic effect of chemical etching and mechanical polishing to efficiently remove excess material from the wafer surface and achieve global nanoscale planarization.

[0007] Polishing slurry is a crucial element in CMP technology, and abrasives are an essential component of the CMP polishing slurry. In the CMP process, abrasives act as cutting agents, homogenizers, chemical reaction aids, and transmitters of mechanical pressure. Driven by the polishing slurry and the carrier's rotational speed, the abrasives grind and destroy the surface of the material to be treated through high-speed impacts, achieving cutting, smoothing, and chemical reactions to the polishing material, thereby achieving the desired surface quality and morphology. Therefore, the type, structure, size, and morphology of the abrasive directly affect the polishing rate and the surface quality of the polished material. The greater the hardness of the polishing particles, the faster the material removal rate per unit time, but it also makes the material surface more susceptible to damage (e.g., scratches, dimensional inhomogeneities) and may trigger stress-induced damage to the material surface.

[0008] Commercial abrasives used in TFLNs primarily consist of solid particles such as silicon oxide, aluminum oxide, and cerium oxide, with Mohs hardnesses of 9 GPa, 7 GPa, and 7 GPa, respectively, all greater than the 5 GPa Mohs hardness of lithium niobate. During the polishing of TFLN devices using these solid particles as abrasives, issues arise regarding size, morphology, and structural uniformity. This not only increases waveguide loss but also leads to difficulties in phase matching. Random phases prevent the construction enhancement of second-order nonlinear optical processes, thus limiting nonlinear efficiency. For example, in a 600 nm TFLN device layer, a thickness variation of only 10 nm is sufficient to cause a phase-matching wavelength shift exceeding 70 nm due to second harmonic generation. Therefore, reducing the hardness of the abrasive can effectively control the surface roughness and uniformity of the TFLN device during polishing, thereby overcoming the limitations imposed by the inherent nanoscale inhomogeneities of TFLN optical waveguides.

[0009] Furthermore, in the currently reported CMP processes for TFLN optical waveguides, the minimum surface roughness is 0.452 nm (greater than the atomic step of 0.205 nm), indicating room for improvement in surface quality. Moreover, existing CMP processes require the use of heavy metal chromium (Cr) as a hard mask, followed by wet etching, which is not only complex but also environmentally polluting. In addition, the lack of active control methods in conventional etching and CMP processes makes obtaining TFLN devices with perfectly vertical walls a continued challenge.

[0010] Therefore, using abrasives with a hardness greater than lithium niobate for planarization of TFLN optical waveguides will affect the device size, morphology and structural uniformity in actual processes, thereby affecting the device's performance.

[0011] Similar problems exist in the fabrication of other thin film structures (e.g., silicon oxide thin films, silicon nitride thin films, etc.) in integrated optical devices.

[0012] There is a need in the art for a method for forming a thin film structure based on integrated optics with improved performance, and for the thin film structure based on integrated optics formed by the method. Summary of the Invention

[0013] This invention is provided to improve the performance of thin-film structures based on integrated optical devices.

[0014] One aspect of the present invention provides a method for forming a thin film structure based on an integrated optical device, comprising: providing a polishing slurry comprising a mesoporous polishing abrasive; providing a sample comprising a substrate, a thin film layer on the substrate, and a hard mask layer on the thin film layer, wherein at least a portion of the thin film layer is exposed; etching the thin film layer to remove at least a portion of the exposed portion of the thin film layer; chemically and mechanically polishing the etched exposed portion of the thin film layer using the polishing slurry comprising the mesoporous polishing abrasive; and removing the hard mask layer.

[0015] The method described above, wherein providing a polishing slurry comprising mesoporous abrasives includes: mixing a surfactant with a polishing abrasive precursor using a soft template method based on sol-gel chemistry to obtain mesoporous polishing abrasives; and configuring the mesoporous polishing abrasives into the polishing slurry comprising the mesoporous polishing abrasives.

[0016] The method described in any of the above methods, wherein the surfactant is retained.

[0017] The method of any of the above, wherein providing a sample comprises: providing a substrate; forming the thin film layer on the substrate; forming the hard mask layer on the thin film layer; and performing patterning to remove at least a portion of the hard mask layer.

[0018] The method described in any of the above embodiments, wherein the hard mask layer does not include chromium, and removing the hard mask layer comprises: using inductively coupled plasma etching (ICP-C) technology.

[0019] The method described in any of the above embodiments, wherein the hardness of the mesoporous polishing abrasive is less than the hardness of the thin film layer, and the hardness of the solid polishing abrasive corresponding to the mesoporous polishing abrasive is greater than the hardness of the thin film layer.

[0020] The method described in any of the above embodiments, wherein the thin film layer comprises a lithium niobate thin film layer; and / or the mesoporous polishing abrasive comprises silicon oxide, aluminum oxide, or cerium oxide.

[0021] Another aspect of the present invention provides a method for forming a thin film structure based on an integrated optical device, comprising: providing a polishing slurry comprising a mesoporous polishing abrasive; providing a sample comprising a substrate and a thin film layer on the substrate; providing a photoresist layer on the thin film layer, wherein at least a portion of the thin film layer is exposed; etching the thin film layer to remove at least a portion of the exposed portion of the thin film layer; chemically and mechanically polishing the etched exposed portion of the thin film layer using the polishing slurry comprising the mesoporous polishing abrasive; and removing the photoresist layer, wherein the hardness of the mesoporous polishing abrasive is less than the hardness of the thin film layer.

[0022] The method described above, wherein providing a polishing slurry comprising mesoporous abrasives includes: mixing a surfactant with a polishing abrasive precursor using a soft template method based on sol-gel chemistry to obtain mesoporous polishing abrasives; and configuring the mesoporous polishing abrasives into the polishing slurry comprising the mesoporous polishing abrasives.

[0023] The method described in any of the above methods, wherein the surfactant is retained.

[0024] The method described in any of the above embodiments, wherein providing the sample includes: providing a substrate; and forming the thin film layer on the substrate.

[0025] The method described in any of the above embodiments, wherein the thin film layer comprises a lithium niobate thin film layer; and / or the mesoporous polishing abrasive comprises silicon oxide, aluminum oxide, or cerium oxide.

[0026] Another aspect of the present invention provides a thin film structure based on integrated optical devices formed by the method described in any of the preceding claims.

[0027] The thin-film structure based on integrated optical devices as described above includes an optical waveguide, an electro-optic modulator, an optical frequency comb, a microring, a microcavity disk, a delay line, or a waveguide amplifier.

[0028] The performance of the thin film structure of the integrated optical device formed according to the method of the present invention and the performance of the corresponding optical device are both improved. Attached Figure Description

[0029] Various embodiments of this application are described in conjunction with the accompanying drawings.

[0030] Figure 1 A flowchart illustrating a method for forming a thin-film structure based on integrated optical devices according to some embodiments of the present invention is shown.

[0031] Figure 2 A schematic diagram illustrating a comparison between a polishing process for a thin-film structure based on integrated optics according to some embodiments of the present invention and an existing polishing process.

[0032] Figure 3 A flowchart illustrating a process for providing a polishing slurry comprising mesoporous polishing abrasives according to some embodiments of the present invention is shown.

[0033] Figure 4 A schematic diagram illustrating a process for providing a mesoporous polishing abrasive according to some embodiments of the present invention is shown.

[0034] Figure 5 A schematic diagram illustrating the process of providing samples according to some embodiments of the present invention is shown.

[0035] Figure 6 A schematic diagram illustrating the process of forming a thin-film structure based on integrated optics according to some embodiments of the present invention is shown.

[0036] Figure 7 A flowchart illustrating a method for forming a thin-film structure based on integrated optical devices according to some embodiments of the present invention is shown.

[0037] Figure 8 A flowchart illustrating a process for providing a polishing slurry comprising mesoporous polishing abrasives according to some embodiments of the present invention is shown.

[0038] Figure 9 A schematic diagram illustrating a process for providing a polishing slurry comprising mesoporous polishing abrasives according to some embodiments of the present invention.

[0039] Figure 10 A schematic diagram illustrating the process of forming a thin-film structure based on integrated optics according to some embodiments of the present invention is shown.

[0040] Figure 11 A schematic diagram of a thin-film structure based on integrated optics formed by a method according to some embodiments of the present invention is shown. Detailed Implementation

[0041] In this application, the term "mesoporous..." refers to a class of porous materials with pore sizes between 2 and 50 nm, as defined by the International Union of Pure and Applied Chemistry.

[0042] In this application, the term "A on B" may include A directly on B (the two are adjacent or in contact), or A above B and other objects may be between A and B.

[0043] Although the embodiments are described primarily with respect to the TFLN structure in this application, the invention is also applicable to other thin film structures, such as silicon oxide thin film structures and silicon nitride thin film structures.

[0044] According to one aspect of the present invention, a method for forming a thin film structure based on integrated optical devices is provided.

[0045] Figure 1 A flowchart illustrating a method 100 for forming a thin-film structure based on integrated optics according to some embodiments of the present invention is shown. The thin-film structure based on integrated optics formed by method 100 may include various on-chip microstructures (e.g., optical waveguides, microrings, microcavity disks and their integrated structures) or other on-chip optics (e.g., high-speed electro-optic modulators, optical frequency combs, delay lines, waveguide amplifiers, etc.).

[0046] Method 100 may include, at block 110, providing a polishing slurry comprising a mesoporous polishing abrasive. In some embodiments, the mesoporous polishing abrasive may include silicon oxide, aluminum oxide, or cerium oxide. In some embodiments, the mesoporous polishing abrasive may be obtained by “pore-forming” a commercially available polishing abrasive (e.g., silicon oxide abrasive, aluminum oxide abrasive, or cerium oxide abrasive). In some embodiments, the step at block 110 may be described below. Figure 3 The process described is implemented as 300, but the scope of the invention is not limited thereto; in alternative embodiments, a prepared polishing slurry comprising mesoporous polishing abrasives may be provided directly.

[0047] Method 100 may include: at block 130, providing a sample, the sample including a substrate, a thin film layer on the substrate, and a hard mask layer on the thin film layer, wherein at least a portion of the thin film layer is exposed. For example, at least a portion of the hard mask layer may be patterned. The step at block 130 may be described below. Figure 5 The process described is implemented as 500, but the scope of the invention is not limited thereto; in alternative embodiments, a prepared sample may be provided directly. As an example, the included portion of the thin film layer (or the patterned portion of the hard mask layer) may correspond to the structure to be formed on the thin film layer.

[0048] In some embodiments, the substrate may include a silicon substrate. In some embodiments, the thin film layer may include a lithium niobate thin film layer (TFLN). In some embodiments, the thin film layer may include a silicon oxide thin film layer, a silicon nitride thin film layer, etc. In some embodiments, the hard mask layer may include a material layer with a hardness (e.g., Mohs hardness) greater than that of the thin film layer. In some embodiments, the hard mask layer may not include chromium. In some embodiments, the hard mask layer may include a silicon oxide layer.

[0049] Optionally, in some embodiments, an intermediate layer (e.g., an oxide layer, such as a silicon oxide layer) may be included on the substrate, and a thin film layer may be formed on the intermediate layer.

[0050] Method 100 may include: at block 150, etching a thin film layer to remove at least a portion of the exposed portion of the thin film layer. As an example, dry etching or wet etching may be used to etch the thin film layer. As an example, the removed portion of the thin film layer may correspond to a structure to be formed. For example, a portion of the thin film layer may be removed to form an optical waveguide, such as a ridge waveguide.

[0051] Method 100 may include: at frame 170, performing chemical mechanical polishing on the etched exposed portion of the thin film layer using a polishing slurry comprising mesoporous polishing abrasives. As an example, the sample may be placed inside a polishing machine and chemically mechanically polished using a polishing slurry comprising mesoporous polishing abrasives. During polishing, the exposed sidewalls of the thin film layer are polished to high precision and high smoothness under the protection of a hard mask layer. The smoothness can be checked using scanning electron microscopy and focused ion beam etching techniques, and polishing can be terminated once design requirements are met.

[0052] Method 100 may include: removing the hard mask layer at frame 190.

[0053] In some embodiments where the hard mask layer does not include chromium (e.g., it includes silicon oxide), removing the hard mask layer may include using an ICP etching technique. Because the hard mask does not include the heavy metal chromium, it is not necessary to use an acidic etching solution for removal, thus ensuring the flatness of the thin film surface after the hard mask layer is removed.

[0054] In some embodiments, method 100 may further include: forming an upper cladding layer on the thin film layer after removing the hard mask layer to protect the thin film layer. As an example, the upper cladding layer may include an oxide layer, such as a silicon oxide layer.

[0055] By using a polishing slurry containing mesoporous polishing abrasives to perform chemical mechanical polishing on the sample, the surface smoothness and sidewall steepness of the formed thin film structure based on integrated optics can be improved.

[0056] For example, the surface smoothness achievable after chemical mechanical polishing of TFLN optical waveguides can be controlled down to a minimum of 0.22 nm, which is close to the atomic step (0.205 nm) and higher than the smoothness achievable by existing processes (approximately 0.45 nm). For example, chemical mechanical polishing of TFLN optical waveguides can achieve a sidewall steepness greater than 75°, thereby reducing transmission loss, which is difficult to achieve in conventional etching processes. For example, the TFLN optical waveguide formed by the method according to embodiments of the present invention not only has extremely low-loss mode coupling efficiency but also a very high quality factor.

[0057] Figure 2 A schematic diagram illustrating a comparison between a polishing process for a thin-film structure based on integrated optics according to some embodiments of the present invention and an existing polishing process.

[0058] During the polishing process, polishing fluid 220 is applied to the polishing pad 210, and downward pressure 240 is applied to the sample carrier plate 230, so that the sample is pressed between the lower side of the sample carrier plate 230 and the top side of the polishing pad 210. When the polishing pad 210 rotates at high speed, the polishing abrasive in the polishing fluid 220 polishes the sample.

[0059] The effect of various types of polishing abrasives on the polishing results is shown at 250. Point a shows defects in the sample material caused by the indentation of irregular abrasives. Protrusions on the abrasive scratch the sample surface, thus creating defects. Point b shows defects in the sample material caused by the indentation of conventional abrasives. Because conventional abrasives are solid and have high hardness, they easily damage the sample surface during polishing, resulting in defects in the sample material. Point c shows a polishing scenario using mesoporous polishing abrasives according to some embodiments of the invention. Because mesoporous polishing abrasives contain a porous structure, their hardness is reduced, thus producing a certain degree of deformation when pressed by the sample carrier, thereby reducing damage to the sample and improving the performance of the polished sample.

[0060] Figure 3 A flowchart illustrating a process 300 for providing a polishing slurry comprising mesoporous polishing abrasives according to some embodiments of the present invention is shown. Process 300 may be a combination of the above. Figure 1 The steps at box 110 in the described method 100 are not limited thereto.

[0061] In some embodiments, process 300 may include: at block 310, mixing a surfactant with a polishing abrasive precursor using a soft template method based on sol-gel chemistry to obtain a mesoporous polishing abrasive. The step at block 310 can be described in conjunction with the following steps. Figure 4 The process described is used to achieve this, but the scope of the invention is not limited thereto.

[0062] In some embodiments, the polishing abrasive to be used to create holes may include commercially available polishing abrasives, such as silicon oxide abrasives, aluminum oxide abrasives, and cerium oxide abrasives, which have Mohs hardnesses of 9 GPa, 7 GPa, and 7 GPa, respectively, all of which are greater than the Mohs hardness of 5 GPa of lithium niobate films.

[0063] In some embodiments, the hardness of the mesoporous polishing abrasive may be less than the hardness of the thin film layer to be polished. In some embodiments, the hardness of the solid polishing abrasive corresponding to the mesoporous polishing abrasive may be greater than the hardness of the thin film layer to be polished. Since the hardness of the mesoporous polishing abrasive is less than the hardness of the thin film layer to be polished (e.g., TFLN), any thin film layer with a higher hardness than the thin film layer (e.g., silicon oxide layer) can be used, thereby avoiding the use of heavy metal chromium, and thus eliminating the need for acidic etching solutions to remove heavy metal chromium, ensuring the flatness of the polished thin film layer, and being economical and environmentally friendly.

[0064] In some embodiments, abrasives of different sizes can be obtained by controlling the feeding, temperature, and time of raw materials (e.g., silicon sources) during the hole-forming process. Among these, smaller abrasives are more convenient for machining recesses.

[0065] In some embodiments, the shape of the polishing particles may include spherical, spiral rod-shaped, etc.

[0066] In some embodiments, process 300 may include: at block 330, configuring a polishing slurry comprising mesoporous polishing abrasive. By adjusting the compatibility of the polishing slurry, crystal orientation etching (CMP) technology for thin film structures (e.g., TFLN structures) can overcome sidewalls with a steepness of 75°, and even achieve completely vertical sidewalls.

[0067] In some embodiments, the surfactant can be retained, i.e., it does not need to be removed. This is because the presence of the surfactant does not increase the hardness of the polishing abrasive, but it can be used to adjust the surface tension of the polishing fluid, disperse the particles of the polishing abrasive, and improve wettability, etc. This allows for improved dispersion of the polishing abrasive in the polishing fluid while avoiding the surfactant removal process.

[0068] Figure 4 A schematic diagram illustrating a process for providing a polishing slurry comprising mesoporous polishing abrasives according to some embodiments of the present invention.

[0069] Raw material 410 (e.g., a silicon source) can be added to solvent 420 containing a surfactant. Subsequently, as shown at 430, solvent 420 containing raw material 410 can be stirred. Subsequently, as shown at 440, the mixture is purified to obtain mesoporous polishing abrasive 450.

[0070] Figure 5 A schematic diagram of a process 500 for providing a sample according to some embodiments of the present invention is shown. Process 500 may be a combination of the above. Figure 1 The steps at box 130 in the described method 100 are not limited thereto.

[0071] In some embodiments, process 500 may include providing a substrate at block 510. As an example, the substrate may include a silicon substrate.

[0072] Optionally, in some embodiments, process 500 may include: forming an intermediate layer on the substrate ( Figure 5 (This step is not shown in the diagram). As an example, physical vapor deposition (PVD) or chemical vapor deposition (CVD) can be used to form the intermediate layer.

[0073] In some embodiments, process 500 may include forming a thin film layer on a substrate at block 530. In embodiments where an intermediate layer is formed, the thin film layer may be formed on the formed intermediate layer; while in embodiments where no intermediate layer is formed, the intermediate layer may be formed directly on the substrate. As an example, PVD or CVD may be used to form the thin film layer. As an example, the thin film layer may include TFLN, silicon oxide film, silicon nitride film, etc.

[0074] In some embodiments, process 500 may include forming a hard mask layer on a thin film layer at block 550. As an example, the hard mask layer may include an oxide layer (e.g., a silicon oxide layer). As an example, PVD or CVD may be used to form the hard mask layer.

[0075] In some embodiments, process 500 may include: at block 570, performing patterning to remove at least a portion of a hard mask layer. The removed portion of the hard mask layer may correspond to a structure to be formed on a thin film layer. As an example, a pattern may be transferred onto the hard mask layer by forming a photoresist layer on the hard mask layer and then patterning the photoresist layer.

[0076] Figure 6 A schematic diagram illustrating the process of forming a thin-film structure based on integrated optics according to some embodiments of the present invention is shown. Figure 6 The process shown can be combined with the above. Figures 1-5 The process described is a specific implementation method, but the process of the present invention is not limited thereto.

[0077] The process begins by providing a substrate 610 at (a). As an example, the substrate 610 may include a silicon substrate. For example, a silicon substrate with a thickness of 500 μm may be formed, but the scope of the invention is not limited thereto.

[0078] The process then proceeds to (b) where an intermediate layer 620 is formed on the substrate 610. As an example, the intermediate layer 620 may include an oxide layer, such as a silicon oxide layer. As an example, PVD or CVD can be used to form the intermediate layer 620. For example, a silicon dioxide layer with a thickness of 2 μm can be formed, but the scope of the invention is not limited thereto. In some embodiments, the step of forming the intermediate layer 620 at (b) may be omitted.

[0079] The process then proceeds to (c) where a thin film layer 630 is formed on the intermediate layer 620. As an example, the thin film layer 630 may include a TFLN. As an example, PVD or CVD can be used to form the thin film layer 630. For example, a TFLN with a thickness of 500-1000 nm can be formed, but the scope of the invention is not limited thereto.

[0080] The process then proceeds to (d) where a hard mask layer 640 is formed on the thin film layer 630. As an example, the hard mask layer 640 may include an oxide layer (e.g., a silicon oxide layer). As an example, PVD or CVD may be used to form the hard mask layer 640.

[0081] The process then proceeds to point (e), where a photoresist layer 650 is formed on the hard mask layer 640. As an example, the photoresist layer 650 can be formed on the hard mask layer 640 by spin coating.

[0082] The process then proceeds to point (f), where patterning is performed to obtain a patterned photoresist layer 650 and a patterned hard mask layer 645. For example, the photoresist layer 650 (see point (e)) can be exposed, developed, and the pattern of the photoresist layer 655 can be transferred to the patterned hard mask layer 645 by etching.

[0083] The process then proceeds to (g), where the patterned photoresist layer 655 is removed (see (f)).

[0084] Subsequently, the process proceeds to (h), where the thin film layer 630 (see (g)) is etched to remove at least a portion of it, thereby obtaining a patterned thin film layer 635. The exposed portions of the patterned thin film layer 635 are then chemically and mechanically polished using a polishing slurry comprising mesoporous polishing abrasives.

[0085] The process then proceeds to (i), where the patterned hard mask layer 645 is removed (see (h)). As an example, ICP can be used to remove the patterned hard mask layer 645.

[0086] The process then proceeds to point (j), where an upper cladding layer 660 is formed on the patterned thin film layer 635. The upper cladding layer 660 can be used to protect the formed patterned thin film layer 645. As an example, the upper cladding layer 660 may include an oxide layer, such as a silicon oxide layer. As an example, PVD or CVD can be used to form the upper cladding layer 660.

[0087] According to another aspect of the present invention, a method for forming a thin film structure based on integrated optical devices is provided.

[0088] Figure 7A flowchart illustrating a method 700 for forming a thin-film structure based on integrated optical devices according to some embodiments of the present invention is shown. Figure 1 Compared to method 100 shown, method 700 may not use a hard mask layer. The thin film structure based on integrated optics formed by method 700 may include various on-chip microstructures (e.g., optical waveguides, microrings, microcavity disks and their integrated structures) or other on-chip optics (e.g., high-speed electro-optic modulators, optical frequency combs, delay lines, waveguide amplifiers, etc.).

[0089] Method 700 may include, at block 710, providing a polishing slurry comprising a mesoporous polishing abrasive. In some embodiments, the mesoporous polishing abrasive may include silicon oxide, aluminum oxide, or cerium oxide. In some embodiments, the mesoporous polishing abrasive may be obtained by “pore-forming” a commercially available polishing abrasive (e.g., silicon oxide abrasive, aluminum oxide abrasive, or cerium oxide abrasive). In some embodiments, the step at block 710 may be described below. Figure 8 The process described is implemented as 800, but the scope of the invention is not limited thereto; in alternative embodiments, a prepared polishing slurry comprising mesoporous polishing abrasives may be provided directly.

[0090] Method 700 may include: at block 720, providing a sample, which may include a substrate and a thin film layer on the substrate. The step at block 720 may be described below. Figure 9 The process described is 900, but the scope of the invention is not limited thereto; in alternative embodiments, a prepared sample may be provided directly. The hardness of the mesoporous polishing abrasive may be less than the hardness of the thin film layer.

[0091] In some embodiments, the substrate may include a silicon substrate. In some embodiments, the thin film layer may include a lithium niobate thin film layer (TFLN). In some embodiments, the thin film layer may include a silicon oxide thin film layer, a silicon nitride thin film layer, etc.

[0092] Optionally, in some embodiments, an intermediate layer (e.g., an oxide layer, such as a silicon oxide layer) may be included on the substrate, and a thin film layer may be formed on the intermediate layer.

[0093] Method 700 may include: at block 730, providing a photoresist layer on the thin film layer, wherein at least a portion of the thin film layer is exposed. As an example, the photoresist layer may be patterned to expose at least a portion of the underlying thin film layer. As an example, the patterned portion of the photoresist layer may correspond to a structure to be formed on the thin film layer.

[0094] Method 700 may include: at block 740, etching a thin film layer to remove at least a portion of the exposed portion of the thin film layer. As an example, dry etching or wet etching may be used to etch the thin film layer. As an example, the removed portion of the thin film layer may correspond to a structure to be formed. For example, a portion of the exposed portion of the thin film layer may be removed to form an optical waveguide, such as a ridge waveguide.

[0095] Method 700 may include: at frame 750, performing chemical mechanical polishing on the etched exposed portion of the thin film layer using a polishing slurry comprising mesoporous polishing abrasive.

[0096] As an example, the sample can be placed in a polishing machine and chemically mechanically polished using a polishing slurry containing mesoporous polishing abrasives to remove at least a portion of the thin film layer. During polishing, the exposed sidewalls of the thin film layer are polished to a high precision and smoothness under the protection of a hard mask layer. The smoothness can be checked using scanning electron microscopy and focused ion beam etching techniques, and polishing can be terminated once design requirements are met.

[0097] Method 700 may include: removing the photoresist layer at box 760.

[0098] In some embodiments, method 700 may further include: forming an upper cladding layer on the thin film layer after removing the photoresist layer to protect the thin film layer. As an example, the upper cladding layer may include an oxide layer, such as a silicon oxide layer.

[0099] By using a polishing slurry containing mesoporous polishing abrasives to perform chemical mechanical polishing on the sample, the surface smoothness and sidewall steepness of the formed thin film structure based on integrated optics can be improved.

[0100] For example, the surface smoothness achievable after chemical mechanical polishing of TFLN optical waveguides can be controlled down to a minimum of 0.22 nm, which is close to the atomic step (0.205 nm) and higher than the smoothness achievable by existing processes (approximately 0.45 nm). For example, chemical mechanical polishing of TFLN optical waveguides can achieve a sidewall steepness greater than 75°, thereby reducing transmission loss, which is difficult to achieve in conventional etching processes. For example, the TFLN optical waveguide formed by the method according to embodiments of the present invention not only has extremely low-loss mode coupling efficiency but also a very high quality factor.

[0101] Furthermore, since the hardness of mesoporous polishing abrasives is less than that of the thin film layer, a hard mask layer is not required for protection when performing chemical mechanical polishing on the thin film layer, which further simplifies the process and saves costs.

[0102] Figure 8 A flowchart illustrating a process 800 for providing a polishing slurry comprising mesoporous polishing abrasives according to some embodiments of the present invention is shown.

[0103] Process 800 can be a combination of the above. Figure 7 The steps at box 710 in the described method 700 are not limited thereto.

[0104] In some embodiments, process 800 may include: at block 810, mixing a surfactant with a polishing abrasive precursor using a soft template method based on sol-gel chemistry to obtain a mesoporous polishing abrasive.

[0105] In some embodiments, the polishing abrasive to be used to create holes may include commercially available polishing abrasives, such as silicon oxide abrasives, aluminum oxide abrasives, and cerium oxide abrasives, which have Mohs hardnesses of 9 GPa, 7 GPa, and 7 GPa, respectively, all of which are greater than the Mohs hardness of 5 GPa of lithium niobate films.

[0106] In some embodiments, the hardness of the mesoporous polishing abrasive may be less than the hardness of the thin film layer to be polished. In some embodiments, the hardness of the solid polishing abrasive corresponding to the mesoporous polishing abrasive may be greater than the hardness of the thin film layer to be polished. Since the hardness of the mesoporous polishing abrasive is less than the hardness of the thin film layer to be polished (e.g., TFLN), any thin film layer with a higher hardness than the thin film layer (e.g., silicon oxide layer) can be used, thereby avoiding the use of heavy metal chromium, and thus eliminating the need for acidic etching solutions to remove heavy metal chromium, ensuring the flatness of the polished thin film layer, and being economical and environmentally friendly.

[0107] In some embodiments, abrasives of different sizes can be obtained by controlling the feeding, temperature, and time of raw materials (e.g., silicon sources) during the hole-forming process. Among these, smaller abrasives are more convenient for machining recesses.

[0108] In some embodiments, the shape of the polishing particles may include spherical, spiral rod-shaped, etc.

[0109] In some embodiments, process 800 may include: at block 830, configuring a polishing slurry comprising mesoporous polishing abrasive. By adjusting the compatibility of the polishing slurry, crystal orientation etching (CMP) technology for thin film structures (e.g., TFLN structures) can overcome sidewalls with a steepness of 75°, and even achieve completely vertical sidewalls.

[0110] In some embodiments, the surfactant can be retained, i.e., it does not need to be removed. This is because the presence of the surfactant does not increase the hardness of the polishing abrasive, but it can be used to adjust the surface tension of the polishing fluid, disperse the particles of the polishing abrasive, and improve wettability, etc. This allows for improved dispersion of the polishing abrasive in the polishing fluid while avoiding the surfactant removal process.

[0111] Figure 9A schematic diagram of a process 900 for providing a sample according to some embodiments of the present invention is shown. Process 900 may be a combination of the above. Figure 7 The steps at box 720 in the described method 700 are not limited thereto.

[0112] In some embodiments, process 900 may include providing a substrate at block 910. As an example, the substrate may include a silicon substrate.

[0113] Optionally, in some embodiments, process 900 may include: forming an intermediate layer on the substrate ( Figure 5 (This step is not shown in the diagram). As an example, PVD or CVD can be used to form the intermediate layer.

[0114] In some embodiments, process 900 may include forming a thin film layer on a substrate at block 930. In embodiments where an intermediate layer is formed, the thin film layer may be formed on the formed intermediate layer; while in embodiments where no intermediate layer is formed, the intermediate layer may be formed directly on the substrate. As an example, PVD or CVD may be used to form the thin film layer. As an example, the thin film layer may include TFLN, silicon oxide film, silicon nitride film, etc.

[0115] Figure 10 A schematic diagram illustrating the process of forming a thin-film structure based on integrated optics according to some embodiments of the present invention is shown. Figure 10 The process shown can be combined with the above. Figures 7-9 The process described is a specific implementation method, but the process of the present invention is not limited thereto.

[0116] The process begins by providing a substrate 1010 at (a). As an example, the substrate 1010 may include a silicon substrate. For example, a silicon substrate with a thickness of 500 μm may be formed, but the scope of the invention is not limited thereto.

[0117] Subsequently, the process proceeds to (b) where an intermediate layer 1020 is formed on the substrate 1010. As an example, the intermediate layer 1020 may include an oxide layer, such as a silicon oxide layer. As an example, PVD or CVD can be used to form the intermediate layer 1020. For example, a silicon dioxide layer with a thickness of 2 μm can be formed, but the scope of the invention is not limited thereto. In some embodiments, the step of forming the intermediate layer 1020 at (b) may be omitted.

[0118] Subsequently, the process proceeds to point (c), where a thin film layer 1030 is formed on the intermediate layer 1020. As an example, the thin film layer 1030 may include a TFLN. As an example, PVD or CVD can be used to form the thin film layer 1030. For example, a TFLN with a thickness of 500-1000 nm can be formed, but the scope of the invention is not limited thereto.

[0119] Subsequently, the process proceeds to point (d), where a photoresist layer 1040 is formed on the thin film layer 1030. As an example, the photoresist layer 1040 can be formed on the thin film layer 1030 by spin coating.

[0120] The process then proceeds to point (e), where patterning is performed to obtain a patterned photoresist layer 1045. For example, the photoresist layer 1040 (see point (d)) may be exposed, developed, and at least a portion of the photoresist layer 1040 may be removed by etching to form the patterned photoresist layer 1045.

[0121] Subsequently, the process proceeds to (f), where the thin film layer 1030 (see (d)) is etched to remove at least a portion of it, thereby obtaining a patterned thin film layer 1035. The exposed portions of the patterned thin film layer 1035 are then chemically and mechanically polished using a polishing slurry comprising mesoporous polishing abrasives.

[0122] The process then proceeds to (g) where the patterned photoresist layer 1045 is removed (see (f)).

[0123] Subsequently, the process proceeds to point (h), where an upper cladding layer 1050 is formed on the patterned thin film layer 1035. The upper cladding layer 1050 can be used to protect the formed patterned thin film layer 1035. As an example, the upper cladding layer 1050 may include an oxide layer, such as a silicon oxide layer. As an example, PVD or CVD can be used to form the upper cladding layer 1050.

[0124] According to another aspect of the present invention, a thin film structure based on integrated optical devices is provided.

[0125] Figure 11 A schematic diagram of a thin-film structure 1100 based on integrated optics, formed by methods according to some embodiments of the present invention, is shown. The thin-film structure 1100 based on integrated optics can be understood by referring to the above description. Figures 1-6 The methods and steps described are formed, or combined with the above. Figures 7-10 The methods and steps described herein are not limited thereto.

[0126] The thin-film structure 1100 based on integrated optical devices may include optical waveguides, electro-optic modulators, optical frequency combs, microrings, microcavity disks, delay lines, or waveguide amplifiers, etc.

[0127] In some embodiments, the thin-film structure 1100 based on integrated optics may include a substrate 1110. As an example, the substrate 1100 may include a silicon substrate.

[0128] In some embodiments, the thin-film structure 1100 based on integrated optics may include an intermediate layer 1120. As an example, the intermediate layer may include an oxide layer, such as a silicon oxide layer. In some embodiments, the intermediate layer 1120 is optional.

[0129] In some embodiments, the thin-film structure 1100 based on integrated optical devices may include a thin-film layer 1130. As an example, the thin-film layer 1130 may include lithium niobate, silicon oxide, or silicon nitride, etc. The structural features of the thin-film layer 1130 can be described in conjunction with the above. Figures 1-6 The methods and steps described, or in combination Figures 7-10 The chemical mechanical polishing steps involved in the described methods and procedures are formed.

[0130] In some embodiments, the thin-film structure 1100 based on integrated optics may include an upper cladding layer 1140. The upper cladding layer 1140 is used to protect the thin-film layer 1130. As an example, the upper cladding layer 1140 may include an oxide layer, such as a silicon oxide layer.

[0131] The thin film layer 1130 obtained by the chemical mechanical polishing process in the methods and steps of embodiments of the present invention has good smoothness (e.g., 0.22 nm, which is close to an atomic step) and good sidewall steepness (e.g., greater than 75°, or even completely perpendicular), which enables the corresponding optical device to have good performance (e.g., extremely low loss mode coupling efficiency, very high quality factor, etc. for TFLN optical waveguides). Therefore, it can be significantly distinguished from thin film structures based on integrated optical devices prepared by prior art.

[0132] Embodiments of this application have been described with reference to the accompanying drawings. These embodiments are illustrative and not restrictive.

Claims

1. A method for forming a thin-film structure based on integrated optical devices, comprising: Polishing fluids containing mesoporous polishing abrasives are provided; Provide a sample comprising a substrate, a thin film layer on the substrate, and a hard mask layer on the thin film layer, wherein at least a portion of the thin film layer is exposed; The thin film layer is etched to remove at least a portion of the exposed portion of the thin film layer; The etched exposed portion of the thin film layer is chemically and mechanically polished using the polishing slurry comprising mesoporous polishing abrasive. as well as Remove the hard mask layer.

2. The method as described in claim 1, wherein, Polishing slurries containing mesoporous abrasives include: Based on sol-gel chemistry, surfactants are mixed with polishing abrasive precursors using a soft template method to obtain mesoporous polishing abrasives; and The mesoporous polishing abrasive is used to prepare the polishing fluid comprising the mesoporous polishing abrasive.

3. The method as described in claim 2, wherein, The surfactant is retained.

4. The method of claim 1, wherein, Samples provided include: Provide substrate; The thin film layer is formed on the substrate; The hard mask layer is formed on the thin film layer; and Perform graphical manipulation to remove at least a portion of the hard mask layer.

5. The method of claim 1, wherein, The hard mask layer does not include chromium, and Removing the hard mask layer includes: Inductively coupled plasma etching technology is used.

6. The method of claim 1, wherein, The hardness of the mesoporous polishing abrasive is less than the hardness of the thin film layer, and The hardness of the solid polishing abrasive corresponding to the mesoporous polishing abrasive is greater than the hardness of the thin film layer.

7. The method of claim 1, wherein, The thin film layer includes a lithium niobate thin film layer; and / or The mesoporous polishing abrasive includes silicon oxide, aluminum oxide, or cerium oxide.

8. A method for forming a thin-film structure based on an integrated optical device, comprising: Polishing fluids containing mesoporous polishing abrasives are provided; Provide a sample, the sample comprising a substrate and a thin film layer on the substrate; A photoresist layer is provided on the thin film layer, wherein at least a portion of the thin film layer is exposed; The thin film layer is etched to remove at least a portion of the exposed portion of the thin film layer; The etched exposed portion of the thin film layer is chemically and mechanically polished using the polishing slurry comprising mesoporous polishing abrasive. as well as Remove the photoresist layer. The hardness of the mesoporous polishing abrasive is less than that of the thin film layer.

9. The method of claim 8, wherein, Polishing slurries containing mesoporous abrasives include: Based on sol-gel chemistry, surfactants are mixed with polishing abrasive precursors using a soft template method to obtain mesoporous polishing abrasives; and The mesoporous polishing abrasive is used to prepare the polishing fluid comprising the mesoporous polishing abrasive.

10. The method of claim 9, wherein, The surfactant is retained.

11. The method of claim 8, wherein, Samples provided include: Provide substrate; and The thin film layer is formed on the substrate.

12. The method of claim 8, wherein, The thin film layer includes a lithium niobate thin film layer; and / or The mesoporous polishing abrasive includes silicon oxide, aluminum oxide, or cerium oxide.

13. A thin-film structure based on integrated optics formed by the method of any one of claims 1-12.

14. The thin-film structure based on integrated optical devices as described in claim 13, wherein, The thin-film structure based on integrated optical devices includes optical waveguides, electro-optic modulators, optical frequency combs, microrings, microcavity disks, delay lines, or waveguide amplifiers.

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