WO2024092422A1 - Wet etching method for thin film lithium niobate, and thin film lithium niobate device - Google Patents

Wet etching method for thin film lithium niobate, and thin film lithium niobate device Download PDF

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WO2024092422A1
WO2024092422A1 PCT/CN2022/128685 CN2022128685W WO2024092422A1 WO 2024092422 A1 WO2024092422 A1 WO 2024092422A1 CN 2022128685 W CN2022128685 W CN 2022128685W WO 2024092422 A1 WO2024092422 A1 WO 2024092422A1
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lithium niobate
film lithium
thin film
micro
thin
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PCT/CN2022/128685
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French (fr)
Chinese (zh)
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李杨
庄荣津
何金泽
祁一凡
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清华大学
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/13—Integrated optical circuits characterised by the manufacturing method
    • G02B6/132—Integrated optical circuits characterised by the manufacturing method by deposition of thin films

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  • the present invention relates to the field of manufacturing photonic devices, and in particular to a wet etching method for thin-film lithium niobate, and a thin-film lithium niobate device obtained by the method.
  • Lithium niobate is a ferroelectric material with a wide transparency window of 350nm to 5000nm, a large refractive index, and chemical and thermal stability.
  • LN due to the non-centrosymmetric lattice of LN, it has a large second-order nonlinear coefficient and electro-optic coefficient, which can achieve high nonlinear wavelength conversion efficiency and low electro-optic modulation driving voltage.
  • LN also exhibits piezoelectric, elastic-optical, birefringent and thermo-optical effects. Based on these excellent photonic properties, LN has been widely used in optoelectronic devices such as electro-optic modulators, acousto-optic modulators, optical frequency combs, and nonlinear wavelength converters.
  • LN is often used as an optical waveguide medium.
  • the method of etching lithium niobate on lithium niobate thin film is usually used to prepare lithium niobate thin film ridge waveguide with small line width.
  • the mainstream micro-nano processing technology for high-quality thin-film lithium niobate is inductively coupled plasma-reactive ion etching (ICP-RIE).
  • ICP-RIE inductively coupled plasma-reactive ion etching
  • This process requires fine adjustment and strict control of relevant parameters during the processing.
  • lithium is considered to be a contaminant element in the CMOS process. Therefore, the micro-nano processing of thin-film lithium niobate based on the ICP-RIE process requires dedicated and expensive plasma etching equipment.
  • the performance indicators of this equipment are heavily dependent on different equipment manufacturers, which reduces the repeatability of the process. Therefore, the ICP-RIE process has the disadvantages of limited throughput, limited process repeatability and high cost.
  • CN 112269225A proposes a wet etching method for lithium niobate thin film waveguide, which includes: after preparing a metal mask with a preset etching shape on the positive domain area of the lithium niobate layer surface in the lithium niobate thin film sample, connecting the lithium niobate thin film sample to be polarized with the metal mask to a polarization circuit, performing domain flipping on the lithium niobate in the area covered by the metal mask, so that the area covered by the metal mask is flipped from the positive domain to the negative domain, fixing the lithium niobate thin film sample after the domain flipping with a preset fixture, and after removing the metal mask on the surface, etching the surface area of the sample after the domain flipping with an etching solution for a preset length of time to obtain a lithium niobate thin film waveguide.
  • CN 112269225A discloses that the method uses the difference in corrosion rate between positive and negative domain
  • the wet etching method uses hydrofluoric acid or a mixed solution of hydrofluoric acid and nitric acid as an etchant.
  • the intermediate layer of the current commercial lithium niobate thin film on insulator (LNOI) is basically a silicon dioxide layer, and this etchant is extremely corrosive to the silicon dioxide layer, which will greatly limit the scope of application and process quality of the wet etching method.
  • the wet etching method requires the use of a metal mask to perform domain flipping on the lithium niobate in the covered area. Since the edges and corners of the electrode often have a higher electric field strength, the area of domain flipping will be larger than the area actually covered by the electrode. Therefore, the wet etching method is not suitable for making narrow slits on +z-cut lithium niobate thin films or narrow waveguides on -z-cut lithium niobate thin films; it is even more difficult to process waveguides and other structures on x-cut lithium niobate thin films.
  • the wet etching method uses the difference in corrosion rate between the positive and negative domains of the lithium niobate crystal in the etchant to prepare lithium niobate thin film waveguides.
  • the edge quality of the domain reversal region depends on the edge quality of the polarization electrode. Compared with the wet etching mask using silicon dioxide in this patent, it is more difficult to achieve high-quality metal mask edges. Therefore, this wet etching method is more difficult to produce high-quality thin-film lithium niobate devices. And the processing accuracy is not as good as photolithography or electron beam exposure.
  • the introduction of the domain reversal process using polarization results in lower efficiency of the wet etching.
  • the inventors of the present invention after intensive research, provide a wet etching method for thin-film lithium niobate, which has the advantages of high quality, high throughput, high process repeatability and low cost, and can achieve mass production of high-fidelity, low-cost integrated lithium niobate photonic devices.
  • the present invention provides a thin film lithium niobate device obtained by the wet etching method, wherein the device has extremely high processing quality and can have a narrow slit structure and a large etching depth.
  • one aspect of the present invention provides a wet etching method for thin-film lithium niobate, the method comprising etching a thin-film lithium niobate wafer using a mixed solution containing H 2 O 2 , NH 4 OH and H 2 O as an etching solution.
  • the wet etching method comprises the following steps:
  • the silicon dioxide thin layer is removed, thereby obtaining the thin film lithium niobate device of the present invention.
  • the thin film lithium niobate wafer in step (1) is a z-tangential thin film lithium niobate wafer.
  • the thickness of the silicon dioxide thin layer in step (1) is 50 nm to 200 nm, preferably 100 nm.
  • the mixing ratio of H 2 O 2 , NH 4 OH and H 2 O in the etching solution in step (4) is 4:3:1 to 1:1:1, preferably 2:2:1.
  • the etching in step (4) is performed at a temperature ranging from 60°C to 90°C, preferably at 85°C.
  • the wet etching method further comprises: annealing the obtained thin film lithium niobate device in a gas environment at a temperature of 150° C. to 300° C. for 1 to 4 hours, preferably annealing in a gas environment at 250° C. for 2 hours.
  • the gas environment may be, but is not limited to, air, oxygen or nitrogen.
  • the etching rate of the wet etching process is greater than 2 nm/min, preferably greater than 3 nm/min, and more preferably greater than 4 nm/min.
  • the etching depth of the lithium niobate layer on the lithium niobate wafer is greater than 200 nm.
  • the present invention provides a thin film lithium niobate device obtained by the above wet etching method.
  • the thin film lithium niobate device includes a ridge waveguide element.
  • the steepness of the side elevation of the ridge waveguide element is between 60° and 70°, and the root mean square roughness of the surface is less than 0.5 nm.
  • the narrowest distance between adjacent ridge waveguide elements is 50 nm to 400 nm.
  • the ridge waveguide element includes a straight waveguide and a micro-ring and/or a micro-track formed by the waveguide, and adjacent ridge waveguide elements refer to adjacent straight waveguides and micro-rings or micro-tracks.
  • the present invention provides a thin film lithium niobate device, comprising a ridge waveguide element etched on a z-cut lithium niobate wafer, wherein the ridge waveguide element includes a straight waveguide and a micro-ring and/or micro-track composed of the waveguide, the straight waveguide and the micro-ring and/or micro-track constitute a coupling element with each other, and the steepness of the side elevation of the ridge waveguide element is between 60° and 70°, the surface root mean square roughness is less than 0.5 nm, and the narrowest distance between the straight waveguide and the micro-ring and/or micro-track constituting the coupling element is 50 nm to 400 nm.
  • the wet etching method has the following technical advantages:
  • the wet etching method has an extremely high etching selectivity ratio for thin-film lithium niobate; therefore, the wet etching method can etch thin-film lithium niobate of any thickness;
  • the wet etching method has strong penetration into the slits and can etch mask slits as narrow as 50 nm, and can avoid the loading effect of dry etching;
  • the obtained thin film lithium niobate device has high processing quality, and its quality factor is as high as 1.21 ⁇ 10 7 .
  • the present invention paves the way for high throughput, low cost, high repeatability and high quality processing of micro-nano structures on thin film lithium niobate.
  • FIG1 shows a schematic flow chart of a wet etching method of the present invention
  • FIG2 is a schematic diagram showing the basic structure of a thin film lithium niobate device of the present invention.
  • Figure 3 shows the measurement results of the quality factors of the micro-rings and micro-tracks on the x- and z-tangential thin film lithium niobate obtained in Examples 1 and 2, wherein Figure 3(a) shows the quality factor curve of Example 1 and Figure 3(b) shows the quality factor curve of Example 2.
  • Figure 4 shows scanning electron microscope images of the cross-section of the thin film lithium niobate ridge waveguide; wherein, Figure 4(a) shows the cross-section of the ridge waveguide of Example 1 in the y direction; Figure 4(b) shows the cross-section of the ridge waveguide of Example 1 in the z direction; Figure 4(c) shows the cross-section of the ridge waveguide of Example 2 in the y direction; Figure 4(d) shows the cross-section of the ridge waveguide of Example 2 in the x direction.
  • FIG. 5 shows a SEM image of a straight waveguide formed in the z-tangential thin film lithium niobate of Example 2 and a slit between the micro-racetracks.
  • thin film lithium niobate device covers all devices with waveguide structures etched in thin film lithium niobate, including but not limited to couplers, beam splitters, gratings, filters, end couplers, photonic crystals, modulators, nonlinear wavelength conversion devices, etc.
  • thin-film lithium niobate wafer covers thin-film lithium niobate structures conventionally used in the art for forming thin-film lithium niobate devices, such as lithium niobate thin films on insulators (LNOI).
  • LNOI lithium niobate thin films on insulators
  • the terms "thin-film lithium niobate wafer” and “thin-film lithium niobate” can be used interchangeably and refer to the same meaning.
  • the present invention provides a method for wet etching of thin-film lithium niobate, the method comprising etching a thin-film lithium niobate wafer using a mixed solution comprising H 2 O 2 , NH 4 OH and H 2 O as an etching solution.
  • the inventors of the present invention have found that by using a mixed solution containing H 2 O 2 , NH 4 OH and H 2 O as an etching solution, an etching rate of 2 nm/min or more, preferably 4 nm/min, can be achieved for a lithium niobate crystal without etching silicon dioxide as a lithium niobate mask; moreover, the wet etching method of the present invention is isotropic for etching each crystal plane of the crystal, so that the properties of thin-film lithium niobate in different tangential directions can be used to achieve anisotropic etching properties, thereby designing different thin-film lithium niobate photonic devices.
  • the lithium niobate layer on the currently commercial lithium niobate on insulator thin film (LNOI) is approximately 300 nm to 900 nm, and the common etching depth is 350 nm; the wet etching method of the present invention can achieve etching of thin films of any thickness within this range, and in particular, can achieve good etching of a depth of more than 200 nm, or more than 350 nm, in particular more than 370 nm, and more particularly more than 400 nm.
  • the wet etching method of the present invention may include:
  • step A Preparing a thin film lithium niobate wafer (step A), and depositing a thin layer of silicon dioxide on one surface of the thin film lithium niobate wafer (step B);
  • step C forming a photoresist coating on the silicon dioxide thin layer, and performing exposure, patterning the photoresist coating (step C), transferring the pattern on the photoresist coating to the silicon dioxide layer (step D), and removing the residual photoresist (step E);
  • step F immerse the thin-film lithium niobate wafer in a mixed solution of H 2 O 2 , NH 4 OH and H 2 O as an etchant for etching (step F); then remove the silicon dioxide thin layer (step G).
  • the wet etching method further comprises annealing the obtained thin film lithium niobate device (step H).
  • the wet etching method has an extremely high etching selectivity ratio for thin-film lithium niobate, so the wet etching method can etch thin-film lithium niobate of any thickness (which is difficult to do in micro-nano processing), thereby achieving a large etching depth; the wet etching method can process multiple wafers at the same time, and all the processes involved are CMOS compatible, so this greatly improves the throughput of thin-film lithium niobate micro-nano processing and greatly reduces the cost. Additional advantages of the wet etching method will be described below.
  • step (A) various thin-film lithium niobate wafers commonly used in the art may be used, such as x-cut thin-film lithium niobate and z-cut thin-film lithium niobate.
  • the wet etching method can produce unexpected etching effects on z-cut lithium niobate, which is mainly manifested in the sidewall properties and abnormally high quality factor of the obtained lithium niobate ridge waveguide.
  • the intrinsic quality factor of the x-cut thin-film lithium niobate device prepared by the wet etching method of the present invention can reach 1.85 ⁇ 10 6
  • the intrinsic quality factor of the z-cut thin-film lithium niobate device can unexpectedly reach 1.21 ⁇ 10 7 , which can exceed the intrinsic quality factor of the best thin-film lithium niobate device obtained by dry etching in the art.
  • a silicon dioxide thin layer can be formed by a deposition method commonly used in the art, such as plasma enhanced chemical vapor deposition (PECVD), and for economic considerations, the silicon dioxide thin layer can be formed into a nanoscale thin layer, for example, with a thickness of 50 nm to 200 nm, preferably about 100 nm.
  • PECVD plasma enhanced chemical vapor deposition
  • the wet etching method has a very high etching selectivity, so the silicon dioxide mask used only needs a very thin thickness, for example, below 200nm, or below 100nm, or about 50nm. Therefore, it is very convenient to process an extremely narrow (about 50nm) slit on the silicon dioxide mask.
  • the mask is too thick, for a narrow slit, the depth-to-width ratio of the silicon dioxide mask will be very large, and the depth-to-width ratio of the electron beam glue used to etch the silicon dioxide mask will also become larger, which will cause the difficulty of the processing technology to increase greatly. Therefore, using a thin silicon dioxide mask is conducive to obtaining a narrow spacing between waveguides in a thin-film lithium niobate device.
  • wet etching uses the solution to directly react chemically with the lithium niobate film, and the reaction product is a substance that dissolves in the etching solution. Since the silicon dioxide mask is relatively thin, the wet etching solution and the lithium niobate film have good wetting and exchange, which is very convenient for etching narrow slits, and also avoids the load effect that exists in the dry etching process.
  • a photoresist coating can be formed by any method known in the art, and then exposed to pattern the photoresist coating.
  • the electron beam glue can be first formed on the silicon dioxide layer by spin coating, and then patterned by electron beam exposure technology, or patterned by photolithography compatible with CMOS process.
  • the electron beam glue can be ZEP 520A or HSQ FOX16.
  • the pattern on the electron beam glue can be transferred to the silicon dioxide layer using an inductively coupled plasma-reactive ion etching process, and the residual electron beam glue can be removed.
  • the process can be performed as follows, and the process of removing the electron beam glue is as follows:
  • the wafer with patterned electron beam glue attached is etched using an inductively coupled plasma-reactive ion etching process. Silicon dioxide is retained where the electron beam glue is covered, and silicon dioxide is completely etched away by the plasma where the electron beam glue is not covered, until the lithium niobate film layer underneath is exposed.
  • the etched wafer is then placed in a degumming solution (such as dimethylformamide) to remove the remaining electron beam glue (such as ZEP 520A).
  • a degumming solution such as dimethylformamide
  • the mixing ratio of H 2 O 2 , NH 4 OH and H 2 O in the etching solution is 4:3:1 to 1:1:1, preferably 3:2:1 to 1:1:1, and more preferably 2:2:1.
  • the etching is performed at a temperature ranging from 60° C. to 90° C., preferably at 85° C.
  • the etching process is performed as follows: using silicon dioxide as a mask, the thin film lithium niobate is immersed in a mixed solution of H 2 O 2 , NH 4 OH and H 2 O in a ratio of 2:2:1 for etching, and the etching temperature is 85° C.
  • step (G) the silicon dioxide mask is removed by, for example, a hydrofluoric acid buffer solution (BOE).
  • a hydrofluoric acid buffer solution BOE
  • the method of removing the silicon dioxide mask is not limited thereto, and a conventional method in the art may be used.
  • step (H) may include: annealing the obtained thin film lithium niobate device in a gas environment such as air, oxygen or nitrogen at a temperature of 150°C to 300°C for 1 to 4 hours, preferably annealing in an air environment at 250°C for 2 hours, so as to repair defects that may be generated during the crystal ion cutting and wet etching process.
  • the annealing process can help to further improve the quality of the obtained lithium niobate thin film device.
  • the above wet etching method can achieve an etching rate of up to about 4 nm/min or more for both x- and z-tangent lithium niobate crystals.
  • the etching rate of the etching solution for the silicon dioxide mask is extremely low. This indicates that the wet etching method has an extremely high etching selectivity for lithium niobate crystals. Therefore, the wet etching method can etch thin films of lithium niobate of any thickness, which is difficult to achieve with micro-nano processing.
  • the wet etching method is particularly suitable for z-tangent lithium niobate crystals.
  • the present invention provides a thin film lithium niobate device obtained by the above wet etching method.
  • a thin-film lithium niobate device comprises a ridge waveguide element etched on a z-tangent lithium niobate wafer, wherein the ridge waveguide element comprises a straight waveguide and a micro-ring and/or micro-track formed by the waveguide, the straight waveguide and the micro-ring and/or micro-track mutually constitute a coupling element, and the steepness of the side elevation of the ridge waveguide element is between 60° and 70°, the surface root mean square roughness is less than 0.5 nm, and the narrowest part between the straight waveguide and the micro-ring and/or micro-track constituting the coupling element is 50 nm to 400 nm.
  • FIG2 shows a schematic diagram of the basic structure of the thin film lithium niobate device of the present invention, wherein FIG2(a) shows a schematic diagram of the thin film lithium niobate device including a straight waveguide and a micro-ring, and FIG2(b) shows a schematic diagram of the thin film lithium niobate device including a straight waveguide and a micro-racetrack.
  • the straight waveguide is represented by a long straight line (partially curved)
  • the micro-ring or micro-racetrack is represented by a circle or annular shape (closed figure).
  • the coupling portion there is a coupling portion between the straight waveguide and the micro-ring or micro-track (corresponding to the portion where the straight line and the ring are tangent in FIG2 ), and the coupling portion corresponds to the narrowest part between the straight waveguide and the micro-ring and/or micro-track, and the spacing can be as low as 50 nm.
  • the suitable spacing range is, for example, 50 nm to 400 nm, preferably 50 nm to 200 nm.
  • the ridge waveguide in the z-cut thin film lithium niobate device has a relatively vertical sidewall, that is, a steepness of 60° to 70°, which provides a basis for the processing of high aspect ratio slits, and in the wet etched device, the sidewall angle is the most critical factor restricting the aspect ratio of the slit.
  • a high slit depth such as more than 400nm
  • a narrow slit width as low as 50nm
  • steepness refers to the angle (in terms of acute angle) between the sidewall of the waveguide and the substrate.
  • the surface root mean square roughness of the side elevation of the ridge waveguide element is less than 0.5 nm, which provides a good basis for providing an excellent quality factor.
  • the surface root mean square roughness is preferably less than 0.5 nm, such as less than 0.45 nm, more preferably less than 0.4 nm.
  • the surface root mean square roughness is preferably greater than 0.1 nm, more preferably greater than 0.2 nm.
  • the micro-ring or micro-track of the thin-film lithium niobate device of the present invention has a very high quality factor, for example, a quality factor of more than 10 6 , and for x-cut thin-film lithium niobate, the quality factor can be as high as 1.85 ⁇ 10 6 , and especially, surprisingly, for z-cut thin-film lithium niobate, it can be as high as 1.21 ⁇ 10 7.
  • the quality factor is the intrinsic quality factor that characterizes the micro-ring or micro-track of the thin-film lithium niobate device.
  • the advantage of the thin film lithium niobate device prepared by the present invention is that, based on the above-mentioned research on wet etching of high-quality waveguides and micro-ring cavities, electro-optic modulators, acousto-optic modulators, thermo-optic modulators, nonlinear wavelength conversion devices, electro-optic frequency combs, Kerr optical frequency combs and other photonic devices based on thin film lithium niobate can be designed. These devices have been widely used in the fields of optical communication, data centers, sensing (ranging, spectral measurement), and optical quantum information processing.
  • Etching solution H 2 O 2 , NH 4 OH and H 2 O commercial reagents, prepared as a 2:2:1 mixed solution
  • Electron beam lithography equipment EBPG 5000plus, Vistec
  • Electron beam glue ZEP 520A, Zeon
  • the spectral scanning system built in the laboratory mainly includes a tunable laser (TSL 550, Santec), a three-paddle polarization controller (FPC560, Thorlabs), three three-axis translation stages (two MAX303/M and one RB13M/M, Thorlabs) and a photodetector (PDA10CS2, Thorlabs)
  • TSL 550 tunable laser
  • FPC560 three-paddle polarization controller
  • PDA10CS2 photodetector
  • Atomic force microscope Dimension FastScan, Bruker
  • the first step of wet etching is to deposit a 100nm thick layer of silicon dioxide on the thin-film lithium niobate wafer (x-cut) using a plasma-enhanced chemical vapor deposition process. Then, the pattern is written on the electron beam glue spun on the silicon dioxide using an electron beam exposure process. Then, the pattern on the electron beam glue is transferred to the silicon dioxide layer by an inductively coupled plasma-reactive ion etching process, and the residual electron beam glue is removed.
  • the thin-film lithium niobate is immersed in a mixed solution of H 2 O 2 , NH 4 OH and H 2 O with a ratio of 2:2:1 for etching, and the etching temperature is 85°C.
  • the silicon dioxide mask is removed using a hydrofluoric acid buffer solution (BOE).
  • the sample is annealed in an air environment at 250°C for 2 hours to repair the defects that may be generated during the crystal ion cutting and wet etching process.
  • the end face of the sample is cut open for the coupling between the optical fiber and the sample later.
  • the wet etching speed is 4nm/min.
  • the straight waveguide and micro-ring are processed by the above-mentioned wet etching process.
  • the thickness of the thin-film lithium niobate is 600nm, and the etching depth is 300nm.
  • the radius of the micro-ring of the x-cut thin-film lithium niobate is 120 ⁇ m.
  • the top width of the waveguide in the micro-ring is 2.6 ⁇ m, and the top width of the coupled waveguide is designed to be 1.4 ⁇ m.
  • the thin film lithium niobate wafer was wet etched by the same method as described in Example 1, except that the thin film lithium niobate wafer was z-tangential.
  • the wet etching rate was also 4 nm/min.
  • the straight waveguide and micro-track were processed by the above-mentioned wet etching process.
  • the thickness of the thin film lithium niobate is 600nm, and the etching depth is 300nm.
  • the radius of the micro-track of the z-tangential thin film lithium niobate is 120 ⁇ m, and the length of the straight part of the micro-track is 3000 ⁇ m.
  • the top width of the coupled waveguide is 1.6 ⁇ m, and the top width of the waveguide in the micro-track is 4 ⁇ m.
  • the dry etching process was performed on the z-cut lithium niobate film (from Jinan NanoLN Company) using RIE etching and CMP polishing process.
  • the specific parameters are: the thickness of the lithium niobate film is 700nm, and the width of the waveguide in the microring is 7 ⁇ m (data from Wolf R, Breunig I, Zappe H, et al. Cascaded second-order optical nonlinearities in on-chip micro rings [J]. Optics express, 2017, 25(24): 29927-29933.).
  • the x-cut lithium niobate film (from Jinan NanoLN Company) was etched using ICP-RIE technology (ICP-RIE is a type of dry etching).
  • ICP-RIE is a type of dry etching.
  • the specific parameters are: the thickness of the lithium niobate film is 600nm, the etching depth is 350nm, and the width of the waveguide in the microtrack is 2.4 ⁇ m (data from Zhang M, Wang C, Cheng R, et al. Monolithic ultra-high-Q lithium niobate microring resonator [J]. Optica, 2017, 4 (12): 1536-1537.).
  • the x-cut lithium niobate film (from Jinan NanoLN) was etched using CMP technology.
  • the specific parameters are: the thickness of the lithium niobate film is 400nm, the processing depth is 400nm, and the width of the waveguide in the microring is 3 ⁇ m (data from Wu R, Wang M, Xu J, et al. Long low-loss-lithium niobate on insulator waveguides with sub-nanometer surface roughness [J]. Nanomaterials, 2018, 8 (11): 910.).
  • the CMP etching method cannot form a straight waveguide and a narrow gap (50 nm) between the microrings.
  • the quality factors of the micro-rings and micro-tracks on the x- and z-tangential thin-film lithium niobate obtained in Examples 1 and 2 were measured.
  • the loading quality factor of the TE 0 mode of the micro-rings on the x-tangential thin-film lithium niobate of Example 1 is up to 1.05 ⁇ 10 6 , and the minimum value of its normalized transmission peak is 0.019. Therefore, the corresponding intrinsic quality factor is 1.85 ⁇ 10 6 .
  • the loading quality factor of the TE 0 mode of the micro-track on the z-cut thin film lithium niobate of Example 2 is up to 8.03 ⁇ 10 6 , and the minimum value of its normalized transmission peak is 0.1058. Therefore, the corresponding intrinsic quality factor is 1.21 ⁇ 10 7 .
  • the shape of the waveguide on the z-cut thin-film lithium niobate is more regular, and its quality factor is higher than the quality factor of the microring on the x-cut thin-film lithium niobate.
  • the above results prove that wet etching can achieve high-quality photonic structures based on thin-film lithium niobate.
  • Comparative Example 1 for the z-tangent thin film lithium niobate, a quality factor of the microring of 3 ⁇ 10 6 was achieved; in Comparative Example 2, for the x-tangent thin film lithium niobate, an intrinsic quality factor of the microring of 1 ⁇ 10 7 was achieved; in Comparative Example 3, for the x-tangent thin film lithium niobate, an intrinsic quality factor of the microring of 1.14 ⁇ 10 7 was achieved, which is the highest quality factor of the microring in this field to date.
  • the quality factor of the thin-film lithium niobate device obtained by the wet etching method of the present invention is similar to the quality factor of the thin-film lithium niobate device obtained by dry etching in the art; in particular, for the z-tangent thin-film lithium niobate device, the quality factor of the present invention (Example 2) is even higher than the quality factor of the z-tangent thin-film lithium niobate device obtained by dry etching and the highest quality factor obtained in the x-tangent thin-film lithium niobate in the art so far.
  • Figure 4 shows the experimental results, wherein Figures 4(a) and (b) are cross-sections of the ridge waveguide on the x-tangential thin-film lithium niobate of Example 1 in the y and z-axis directions; and Figures 4(c) and (d) are cross-sections of the ridge waveguide on the z-tangential thin-film lithium niobate of Example 2 in the y and x-axis directions.
  • the sidewall edges in the ⁇ y direction and -z direction are curved, and the sidewalls in the +z direction are relatively vertical with an angle of 85° ( Figures 4(a) and (b)).
  • the edges of all sidewalls are straight lines.
  • the angles of the side walls in the ⁇ x and +y directions are approximately 60°, and the angle of the side walls in the -y direction is approximately 70° (Fig. 4(c) and (d)).
  • FIG5 shows an SEM image of the slits formed in the z-tangential thin-film lithium niobate of Example 2.
  • Comparative Example 3 since the steepness of the waveguide sidewall polished by CMP is generally relatively small, a relatively large etching depth is required to better confine the light. At the same time, since the steepness of the waveguide sidewall polished by CMP is relatively small, it is believed that a narrow slit cannot be formed in Comparative Example 3.
  • the slit depth can be formed to be greater than 200 nm, for example, greater than 400 nm.
  • the surface roughness of the waveguide in the thin-film lithium niobate device formed in Examples 1 and 2 was tested.
  • the surface of the sample was tested using an atomic force microscope (Dimension FastScan, Bruker), and the working mode was peak force tapping mode.
  • the root mean square roughness and coherence length were used to characterize the surface roughness of the waveguide in the thin-film lithium niobate device.
  • the experimental results obtained are shown in Table 1 below.
  • the surface RMS roughness of the thin film lithium niobate (waveguide side wall) after wet etching does not increase much, and remains below 0.5 nm.
  • Such surface roughness maintains a good quality factor (as measured in Experimental Example 1 above), and together with the steepness of the waveguide side wall, provides a good basis for obtaining a slit with a high aspect ratio.

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Abstract

The present invention relates to a wet etching method for thin film lithium niobate, and a thin film lithium niobate device. The wet etching method of the present invention comprises: etching a thin film lithium niobate wafer by using a mixture solution containing H2O2, NH4OH, and H2O as an etchant, wherein a silicon dioxide thin layer is used as an etching mask, so as to form the thin film lithium niobate device having a narrow slit. The steepness of a lateral facade of a ridge waveguide element in the thin film lithium niobate device of the present invention is 60° to 70°, the root mean square roughness of the surface is 0.5 nm or below, and thus the thin film lithium niobate device of the present invention can have a quality factor of up to 1.21×107.

Description

薄膜铌酸锂的湿法刻蚀方法及薄膜铌酸锂器件Wet etching method for thin film lithium niobate and thin film lithium niobate device 技术领域Technical Field
本发明涉及光子学器件的制造领域，具体而言，本发明涉及一种薄膜铌酸锂的湿法刻蚀方法，以及由该方法获得的薄膜铌酸锂器件。The present invention relates to the field of manufacturing photonic devices, and in particular to a wet etching method for thin-film lithium niobate, and a thin-film lithium niobate device obtained by the method.
背景技术Background technique
铌酸锂(LN)是一种铁电材料，其具有350nm至5000nm的宽透明窗口、较大的折射率，以及化学和热稳定性。此外，由于LN的非中心对称晶格，其具有较大的二阶非线性系数和电光系数，可以实现高非线性波长转换效率和低电光调制驱动电压。此外，LN还表现出压电、弹性光学、双折射和热光学效应。基于这些优异的光子特性，LN已广泛应用于电光调制器、声光调制器、光频梳、非线性波长转换器等光电器件。Lithium niobate (LN) is a ferroelectric material with a wide transparency window of 350nm to 5000nm, a large refractive index, and chemical and thermal stability. In addition, due to the non-centrosymmetric lattice of LN, it has a large second-order nonlinear coefficient and electro-optic coefficient, which can achieve high nonlinear wavelength conversion efficiency and low electro-optic modulation driving voltage. In addition, LN also exhibits piezoelectric, elastic-optical, birefringent and thermo-optical effects. Based on these excellent photonic properties, LN has been widely used in optoelectronic devices such as electro-optic modulators, acousto-optic modulators, optical frequency combs, and nonlinear wavelength converters.
如今，LN常用于光波导介质。随着近年来LN薄膜制备工艺的日趋完善，通常采用在铌酸锂薄膜上对铌酸锂进行刻蚀的方法，来制备线宽较小的铌酸锂薄膜脊型波导。Nowadays, LN is often used as an optical waveguide medium. With the improvement of LN thin film preparation technology in recent years, the method of etching lithium niobate on lithium niobate thin film is usually used to prepare lithium niobate thin film ridge waveguide with small line width.
目前，高品质的薄膜铌酸锂(TFLN)的主流微纳加工工艺是电感耦合等离子体-反应离子刻蚀(ICP-RIE)。该工艺需要精细的调节和严格的控制加工过程中的相关参数。除此之外，锂元素被认为是CMOS工艺过程中的污染元素。因此，基于ICP-RIE工艺的薄膜铌酸锂的微纳加工需要专用的、昂贵的等离子体刻蚀设备。然而，该设备的性能指标严重依赖于不同的设备制造商，从而降低了该工艺的可重复性。因此，ICP-RIE工艺具有吞吐量有限，工艺重复性有限和高成本的劣势。At present, the mainstream micro-nano processing technology for high-quality thin-film lithium niobate (TFLN) is inductively coupled plasma-reactive ion etching (ICP-RIE). This process requires fine adjustment and strict control of relevant parameters during the processing. In addition, lithium is considered to be a contaminant element in the CMOS process. Therefore, the micro-nano processing of thin-film lithium niobate based on the ICP-RIE process requires dedicated and expensive plasma etching equipment. However, the performance indicators of this equipment are heavily dependent on different equipment manufacturers, which reduces the repeatability of the process. Therefore, the ICP-RIE process has the disadvantages of limited throughput, limited process repeatability and high cost.
CN 112269225A提出了一种铌酸锂薄膜波导的湿法刻蚀方法，其包括：在铌酸锂薄膜样品中的铌酸锂层表面正畴区域上制备具有预设刻蚀形状的金属掩膜后，将具备金属掩膜的待极化铌酸锂薄膜样品接入极化电路，对金属掩膜覆盖区域的铌酸锂进行畴翻转，使得金属掩膜覆盖区域由正畴翻转为负畴，利用预设夹具固定住畴翻转后的铌酸锂薄膜样品，并去除表面的金属掩膜后，利用刻蚀溶液对畴翻转后样品的表面区域进行预设时长的刻蚀，得到铌酸锂薄膜波导。CN 112269225A公开了，其方法利用正负畴的腐蚀速度差异来制备铌酸锂薄膜波导。CN 112269225A proposes a wet etching method for lithium niobate thin film waveguide, which includes: after preparing a metal mask with a preset etching shape on the positive domain area of the lithium niobate layer surface in the lithium niobate thin film sample, connecting the lithium niobate thin film sample to be polarized with the metal mask to a polarization circuit, performing domain flipping on the lithium niobate in the area covered by the metal mask, so that the area covered by the metal mask is flipped from the positive domain to the negative domain, fixing the lithium niobate thin film sample after the domain flipping with a preset fixture, and after removing the metal mask on the surface, etching the surface area of the sample after the domain flipping with an etching solution for a preset length of time to obtain a lithium niobate thin film waveguide. CN 112269225A discloses that the method uses the difference in corrosion rate between positive and negative domains to prepare lithium niobate thin film waveguides.
然而，上述湿法刻蚀方法的制备过程过于复杂，不利于铌酸锂薄膜波导的大规模量产。具体如下：(1)该湿法刻蚀方法用氢氟酸或者氢氟酸和硝酸的混合溶液做刻蚀剂， 目前商用的绝缘体上铌酸锂薄膜(LNOI)中间层基本都是二氧化硅层，而这种刻蚀剂对二氧化硅层有极强的腐蚀性，会大大限制该湿法刻蚀方法的适用范围和工艺质量。(2)该湿法刻蚀方法需要利用金属掩模对覆盖区域的铌酸锂进行畴翻转，由于电极的边缘和尖角处往往具有更高的电场强度，导致畴翻转的区域会大于电极实际覆盖的区域，因此该湿法刻蚀方法不宜在+z切的铌酸锂薄膜上制造窄狭缝或在-z切的铌酸锂薄膜上制造窄波导；更是很难在x切铌酸锂薄膜上加工波导等结构。(3)该湿法刻蚀方法利用铌酸锂晶体正负畴在刻蚀剂中的腐蚀速度差异来制备铌酸锂薄膜波导。畴翻转区域的边缘质量取决于极化电极的边缘的质量。相较于本专利中通过二氧化硅做湿法刻蚀的掩模，想要实现高质量的金属掩模边缘是更难的。因此，这种湿法刻蚀的方法更难制作出高质量的薄膜铌酸锂器件。且加工精度也不如光刻或电子束曝光。(4)电极化实现畴翻转工艺的引入导致该湿法刻蚀的效率较低。However, the preparation process of the above-mentioned wet etching method is too complicated, which is not conducive to the large-scale mass production of lithium niobate thin film waveguides. Specifically: (1) The wet etching method uses hydrofluoric acid or a mixed solution of hydrofluoric acid and nitric acid as an etchant. The intermediate layer of the current commercial lithium niobate thin film on insulator (LNOI) is basically a silicon dioxide layer, and this etchant is extremely corrosive to the silicon dioxide layer, which will greatly limit the scope of application and process quality of the wet etching method. (2) The wet etching method requires the use of a metal mask to perform domain flipping on the lithium niobate in the covered area. Since the edges and corners of the electrode often have a higher electric field strength, the area of domain flipping will be larger than the area actually covered by the electrode. Therefore, the wet etching method is not suitable for making narrow slits on +z-cut lithium niobate thin films or narrow waveguides on -z-cut lithium niobate thin films; it is even more difficult to process waveguides and other structures on x-cut lithium niobate thin films. (3) The wet etching method uses the difference in corrosion rate between the positive and negative domains of the lithium niobate crystal in the etchant to prepare lithium niobate thin film waveguides. The edge quality of the domain reversal region depends on the edge quality of the polarization electrode. Compared with the wet etching mask using silicon dioxide in this patent, it is more difficult to achieve high-quality metal mask edges. Therefore, this wet etching method is more difficult to produce high-quality thin-film lithium niobate devices. And the processing accuracy is not as good as photolithography or electron beam exposure. (4) The introduction of the domain reversal process using polarization results in lower efficiency of the wet etching.
为此，本领域还需要一种简单和低成本的铌酸锂薄膜的制备方法，其在保证所得薄膜的品质的同时，还有利于大规模量产。Therefore, there is a need in the art for a simple and low-cost method for preparing a lithium niobate thin film, which can ensure the quality of the obtained thin film while being conducive to large-scale mass production.
发明内容Summary of the invention
有鉴于此，本发明的发明人经潜心研究，提供了一种薄膜铌酸锂的湿法刻蚀方法，该方法具有高品质、高吞吐量、高工艺可重复性和低成本的优势，并且能够实现高保真度、低成本的集成铌酸锂光子学器件的量产。In view of this, the inventors of the present invention, after intensive research, provide a wet etching method for thin-film lithium niobate, which has the advantages of high quality, high throughput, high process repeatability and low cost, and can achieve mass production of high-fidelity, low-cost integrated lithium niobate photonic devices.
另一方面，本发明提供了一种由上述湿法刻蚀方法获得的薄膜铌酸锂器件，所述器件具有极高的加工品质，并且能够具有窄狭缝构造和大的刻蚀深度。On the other hand, the present invention provides a thin film lithium niobate device obtained by the wet etching method, wherein the device has extremely high processing quality and can have a narrow slit structure and a large etching depth.
为此，本发明的一个方面提供了一种薄膜铌酸锂的湿法刻蚀方法，所述方法包括利用包含H 2O 2、NH 4OH和H 2O的混合溶液作为刻蚀液对薄膜铌酸锂晶圆进行刻蚀。 To this end, one aspect of the present invention provides a wet etching method for thin-film lithium niobate, the method comprising etching a thin-film lithium niobate wafer using a mixed solution containing H 2 O 2 , NH 4 OH and H 2 O as an etching solution.
在本发明的实施方式中，所述湿法刻蚀方法包括以下步骤：In an embodiment of the present invention, the wet etching method comprises the following steps:
(1)准备薄膜铌酸锂晶圆，并在该薄膜铌酸锂晶圆的一个表面上沉积二氧化硅薄层；(1) preparing a thin-film lithium niobate wafer and depositing a thin layer of silicon dioxide on one surface of the thin-film lithium niobate wafer;
(2-a)在二氧化硅薄层上形成光刻胶涂层，并进行曝光，将光刻胶涂层图案化；(2-a) forming a photoresist coating on the silicon dioxide thin layer, and performing exposure to light to pattern the photoresist coating;
(2-b)将光刻胶涂层上的图案转移至二氧化硅层上，并除去残余的光刻胶；(2-b) transferring the pattern on the photoresist coating to the silicon dioxide layer and removing the residual photoresist;
(3)利用图案化的二氧化硅薄层作为掩模，将薄膜铌酸锂晶圆浸入作为刻蚀液的H 2O 2、NH 4OH和H 2O的混合溶液中进行刻蚀； (3) using the patterned silicon dioxide thin layer as a mask, immersing the thin film lithium niobate wafer in a mixed solution of H 2 O 2 , NH 4 OH and H 2 O as an etching solution for etching;
(4)湿法刻蚀结束后，去除二氧化硅薄层，由此得到本发明的薄膜铌酸锂器件。(4) After the wet etching is completed, the silicon dioxide thin layer is removed, thereby obtaining the thin film lithium niobate device of the present invention.
在一个实施方式中，步骤(1)中的薄膜铌酸锂晶圆是z切向薄膜铌酸锂晶圆。In one embodiment, the thin film lithium niobate wafer in step (1) is a z-tangential thin film lithium niobate wafer.
在一个实施方式中，步骤(1)中的二氧化硅薄层的厚度为50nm至200nm，优选为100nm。In one embodiment, the thickness of the silicon dioxide thin layer in step (1) is 50 nm to 200 nm, preferably 100 nm.
在一个实施方式中，步骤(4)中的刻蚀液中H 2O 2、NH 4OH和H 2O的混合比为4:3:1至1:1:1，优选为2:2:1。 In one embodiment, the mixing ratio of H 2 O 2 , NH 4 OH and H 2 O in the etching solution in step (4) is 4:3:1 to 1:1:1, preferably 2:2:1.
在一个实施方式中，步骤(4)中的刻蚀在60℃至90℃的范围下进行，优选在85℃进行。In one embodiment, the etching in step (4) is performed at a temperature ranging from 60°C to 90°C, preferably at 85°C.
在一个实施方式中，上述湿法刻蚀方法还包括：将所得的薄膜铌酸锂器件在150℃至300℃的温度的气体环境中退火1至4小时，优选在250℃的气体环境中退火2小时。In one embodiment, the wet etching method further comprises: annealing the obtained thin film lithium niobate device in a gas environment at a temperature of 150° C. to 300° C. for 1 to 4 hours, preferably annealing in a gas environment at 250° C. for 2 hours.
在一个具体实施例中，所述气体环境可以是但不限于空气、氧气或氮气。In a specific embodiment, the gas environment may be, but is not limited to, air, oxygen or nitrogen.
在一个实施方式中，所述湿法刻蚀过程的刻蚀速度是2nm/min以上，优选3nm/min以上，更优选为4nm/min以上。In one embodiment, the etching rate of the wet etching process is greater than 2 nm/min, preferably greater than 3 nm/min, and more preferably greater than 4 nm/min.
在一个实施方式中，所述铌酸锂晶圆上的铌酸锂层的刻蚀深度为200nm以上。In one embodiment, the etching depth of the lithium niobate layer on the lithium niobate wafer is greater than 200 nm.
另一方面，本发明提供了由上述湿法刻蚀方法获得的薄膜铌酸锂器件。On the other hand, the present invention provides a thin film lithium niobate device obtained by the above wet etching method.
在一个实施方式中，所述薄膜铌酸锂器件包括脊状波导元件。In one embodiment, the thin film lithium niobate device includes a ridge waveguide element.
在一个实施方式中，所述脊状波导元件的侧立面的陡度为60°至70°之间，表面均方根粗糙度为0.5nm以下。In one embodiment, the steepness of the side elevation of the ridge waveguide element is between 60° and 70°, and the root mean square roughness of the surface is less than 0.5 nm.
在一个实施方式中，相邻的脊状波导元件之间最窄处的间距为50nm至400nm。In one embodiment, the narrowest distance between adjacent ridge waveguide elements is 50 nm to 400 nm.
在一个实施方式中，所述脊状波导元件包括直波导以及由波导构成的微环和/或微跑道，并且相邻的脊状波导元件是指相邻的直波导和微环或微跑道。In one embodiment, the ridge waveguide element includes a straight waveguide and a micro-ring and/or a micro-track formed by the waveguide, and adjacent ridge waveguide elements refer to adjacent straight waveguides and micro-rings or micro-tracks.
在另一方面中，本发明提供了一种薄膜铌酸锂器件，其包含在z切向铌酸锂晶圆上刻蚀得到的脊状波导元件，其中，所述脊状波导元件包括直波导以及由波导构成的微环和/或微跑道，所述直波导与所述微环和/或微跑道相互构成耦合元件，并且所述脊状波导元件的侧立面的陡度为60°至70°之间，表面均方根粗糙度为0.5nm以下，构成耦合元件的直波导与微环和/或微跑道之间的最窄处的间距50nm至400nm。In another aspect, the present invention provides a thin film lithium niobate device, comprising a ridge waveguide element etched on a z-cut lithium niobate wafer, wherein the ridge waveguide element includes a straight waveguide and a micro-ring and/or micro-track composed of the waveguide, the straight waveguide and the micro-ring and/or micro-track constitute a coupling element with each other, and the steepness of the side elevation of the ridge waveguide element is between 60° and 70°, the surface root mean square roughness is less than 0.5 nm, and the narrowest distance between the straight waveguide and the micro-ring and/or micro-track constituting the coupling element is 50 nm to 400 nm.
根据本发明，所述湿法刻蚀方法具有以下技术优势：According to the present invention, the wet etching method has the following technical advantages:
(a)该湿法刻蚀方法对薄膜铌酸锂具有极高的刻蚀选择比；因此，该湿法刻蚀方法可以对任意厚度的薄膜铌酸锂进行刻蚀；(a) The wet etching method has an extremely high etching selectivity ratio for thin-film lithium niobate; therefore, the wet etching method can etch thin-film lithium niobate of any thickness;
(b)该湿法刻蚀方法对狭缝具有很强的穿透性，可以对窄至50nm的掩模狭缝进行刻蚀，并能够避免干法刻蚀的负载效应；(b) The wet etching method has strong penetration into the slits and can etch mask slits as narrow as 50 nm, and can avoid the loading effect of dry etching;
(c)湿法刻蚀可以同时处理多个晶圆，这极大的提高了薄膜铌酸锂微纳加工的吞吐量并降低了成本；(c) Wet etching can process multiple wafers simultaneously, which greatly improves the throughput of thin-film lithium niobate micro-nano processing and reduces costs;
(d)由于湿法蚀刻的薄膜铌酸锂的器件结构的品质仅取决于易于获得的湿法蚀刻溶剂和薄膜铌酸锂晶圆，因此该方法具有高度可重复性；(d) The method is highly reproducible because the quality of the device structure of the wet-etched thin-film lithium niobate depends only on the readily available wet etching solvent and thin-film lithium niobate wafers;
(e)所得的薄膜铌酸锂器件具有高加工品质，其品质因子最高达1.21×10 7。 (e) The obtained thin film lithium niobate device has high processing quality, and its quality factor is as high as 1.21×10 7 .
因此，本发明为高吞吐量、低成本、高可重复性和高质量薄膜铌酸锂上微纳结构的加工铺平了道路。Therefore, the present invention paves the way for high throughput, low cost, high repeatability and high quality processing of micro-nano structures on thin film lithium niobate.
附图说明BRIEF DESCRIPTION OF THE DRAWINGS
本发明所描述的附图仅为了说明选定的实施例的目的，而不是所有可能的实施方式，而并非意在限制本发明的范围。在附图中：The accompanying drawings described in the present invention are only for the purpose of illustrating selected embodiments, not all possible implementations, and are not intended to limit the scope of the present invention. In the accompanying drawings:
图1示出了本发明的湿法刻蚀方法的示意性流程图；FIG1 shows a schematic flow chart of a wet etching method of the present invention;
图2示出了本发明的薄膜铌酸锂器件的基本结构的示意图；FIG2 is a schematic diagram showing the basic structure of a thin film lithium niobate device of the present invention;
图3示出了实施例1和2中获得的x-和z切向薄膜铌酸锂上的微环和微跑道的品质因子的测量结果，其中，图3(a)示出了实施例1的品质因子曲线，图3(b)示出了实施例2的品质因子曲线。Figure 3 shows the measurement results of the quality factors of the micro-rings and micro-tracks on the x- and z-tangential thin film lithium niobate obtained in Examples 1 and 2, wherein Figure 3(a) shows the quality factor curve of Example 1 and Figure 3(b) shows the quality factor curve of Example 2.
图4示出了薄膜铌酸锂脊状波导的横截面的扫描电子显微镜图；其中，图4(a)示出了实施例1的脊状波导在y方向的横截面；图4(b)示出了实施例1的脊状波导在z方向的横截面；图4(c)示出了实施例2的脊状波导在y方向的横截面；图4(d)示出了实施例2的脊状波导在x方向的横截面。Figure 4 shows scanning electron microscope images of the cross-section of the thin film lithium niobate ridge waveguide; wherein, Figure 4(a) shows the cross-section of the ridge waveguide of Example 1 in the y direction; Figure 4(b) shows the cross-section of the ridge waveguide of Example 1 in the z direction; Figure 4(c) shows the cross-section of the ridge waveguide of Example 2 in the y direction; Figure 4(d) shows the cross-section of the ridge waveguide of Example 2 in the x direction.
图5示出了实施例2的z切向薄膜铌酸锂中形成的直波导和微跑道之间的狭缝的SEM图。FIG. 5 shows a SEM image of a straight waveguide formed in the z-tangential thin film lithium niobate of Example 2 and a slit between the micro-racetracks.
具体实施方式Detailed ways
在下文中，将更详细地描述本发明。Hereinafter, the present invention will be described in more detail.
应当理解，说明书和权利要求书中使用的术语可以基于发明人可以适当地定义的原则，而解释为具有与其在相关领域和本发明的技术构思的背景下的含义一致的含义。说明书中使用的术语仅用于解释示例性实施方式，并非意在限制本发明。It should be understood that the terms used in the specification and claims can be interpreted as having a meaning consistent with its meaning in the context of the relevant field and the technical concept of the present invention based on the principle that the inventor can appropriately define. The terms used in the specification are only used to explain the exemplary embodiments and are not intended to limit the present invention.
进一步应理解，当在本说明书中使用时，术语“包括”、“包含”或“具有”指明所陈述的特征、数字、步骤、要素或其组合的存在，但并不排除一个或多个其他特征、数字、 步骤、要素或其组合的存在或加入。It should be further understood that when used in this specification, the terms "include", "comprises" or "has" indicate the presence of stated features, numbers, steps, elements or a combination thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements or a combination thereof.
在本文中，在参考附图描述元件的结构时，在描述某一部件的位置关系时，“上”、“下”、“上层”、“下层”等是指该部件的相对位置关系，而非限制于附图中所示的结构。In this article, when describing the structure of an element with reference to the accompanying drawings, when describing the positional relationship of a certain component, "upper", "lower", "upper layer", "lower layer" and the like refer to the relative positional relationship of the components, and are not limited to the structure shown in the accompanying drawings.
在本发明中，术语“薄膜铌酸锂器件”涵盖了包含在薄膜铌酸锂中刻蚀出的具有波导结构的所有器件，其包括但不限于耦合器，分束器，光栅，滤波器，端面耦合器，光子晶体，调制器，非线性波长转换器件等。In the present invention, the term "thin film lithium niobate device" covers all devices with waveguide structures etched in thin film lithium niobate, including but not limited to couplers, beam splitters, gratings, filters, end couplers, photonic crystals, modulators, nonlinear wavelength conversion devices, etc.
术语“薄膜铌酸锂晶圆”涵盖本领域中常规使用的用于形成薄膜铌酸锂器件的薄膜铌酸锂结构，例如绝缘体上铌酸锂薄膜(LNOI)。另外，在涉及刻蚀方法的步骤时，术语“薄膜铌酸锂晶圆”和“薄膜铌酸锂”可相互使用，并指代同样的含义。The term "thin-film lithium niobate wafer" covers thin-film lithium niobate structures conventionally used in the art for forming thin-film lithium niobate devices, such as lithium niobate thin films on insulators (LNOI). In addition, when referring to the steps of the etching method, the terms "thin-film lithium niobate wafer" and "thin-film lithium niobate" can be used interchangeably and refer to the same meaning.
在一个方面中，概括而言，本发明提供了一种薄膜铌酸锂的湿法刻蚀方法，所述方法包括利用包含H 2O 2、NH 4OH和H 2O的混合溶液作为刻蚀液对薄膜铌酸锂晶圆进行刻蚀。 In one aspect, in summary, the present invention provides a method for wet etching of thin-film lithium niobate, the method comprising etching a thin-film lithium niobate wafer using a mixed solution comprising H 2 O 2 , NH 4 OH and H 2 O as an etching solution.
本发明的发明人发现，通过利用包含H 2O 2、NH 4OH和H 2O的混合溶液作为刻蚀液，可以实现针对铌酸锂晶体的2nm/min以上、优选4nm/min的刻蚀，而不会刻蚀作为铌酸锂掩模的二氧化硅；而且，本发明的湿法刻蚀方法对于晶体的各个晶面的刻蚀是各向同性的，因而可以利用不同切向的薄膜铌酸锂的性质实现各向异性的刻蚀性质，由此进行不同的薄膜铌酸锂光子学器件的设计。此外，目前商用的绝缘体上铌酸锂薄膜(LNOI)上的铌酸锂层大致为300nm至900nm，而常见的刻蚀深度为350nm；本发明的湿法刻蚀方法可以实现该范围内任意厚度的薄膜的刻蚀，特别是，可以实现200nm以上、或350nm以上、特别是370nm以上、更特别400nm以上深度的良好刻蚀。 The inventors of the present invention have found that by using a mixed solution containing H 2 O 2 , NH 4 OH and H 2 O as an etching solution, an etching rate of 2 nm/min or more, preferably 4 nm/min, can be achieved for a lithium niobate crystal without etching silicon dioxide as a lithium niobate mask; moreover, the wet etching method of the present invention is isotropic for etching each crystal plane of the crystal, so that the properties of thin-film lithium niobate in different tangential directions can be used to achieve anisotropic etching properties, thereby designing different thin-film lithium niobate photonic devices. In addition, the lithium niobate layer on the currently commercial lithium niobate on insulator thin film (LNOI) is approximately 300 nm to 900 nm, and the common etching depth is 350 nm; the wet etching method of the present invention can achieve etching of thin films of any thickness within this range, and in particular, can achieve good etching of a depth of more than 200 nm, or more than 350 nm, in particular more than 370 nm, and more particularly more than 400 nm.
具体而言，参见图1，其示出了本发明的湿法刻蚀方法的示意性流程图。本发明的湿法刻蚀方法可以包括：Specifically, referring to FIG1 , a schematic flow chart of the wet etching method of the present invention is shown. The wet etching method of the present invention may include:
-准备薄膜铌酸锂晶圆(步骤A)，并在该薄膜铌酸锂晶圆的一个表面上沉积二氧化硅薄层(步骤B)；- Preparing a thin film lithium niobate wafer (step A), and depositing a thin layer of silicon dioxide on one surface of the thin film lithium niobate wafer (step B);
-在二氧化硅薄层上形成光刻胶涂层，并进行曝光，将光刻胶涂层图案化(步骤C)，并将光刻胶涂层上的图案转移至二氧化硅层上(步骤D)，并除去残余的光刻胶(步骤E)；- forming a photoresist coating on the silicon dioxide thin layer, and performing exposure, patterning the photoresist coating (step C), transferring the pattern on the photoresist coating to the silicon dioxide layer (step D), and removing the residual photoresist (step E);
-利用图案化的二氧化硅薄层作为掩模，将薄膜铌酸锂晶圆浸入作为刻蚀液的H 2O 2、NH 4OH和H 2O的混合溶液中进行刻蚀(步骤F)；然后除去二氧化硅薄层(步骤G)。 - Using the patterned silicon dioxide thin layer as a mask, immerse the thin-film lithium niobate wafer in a mixed solution of H 2 O 2 , NH 4 OH and H 2 O as an etchant for etching (step F); then remove the silicon dioxide thin layer (step G).
可选地，该湿法刻蚀方法还包括，将所得的薄膜铌酸锂器件退火(步骤H)。Optionally, the wet etching method further comprises annealing the obtained thin film lithium niobate device (step H).
如上所述，该湿法刻蚀方法该对薄膜铌酸锂具有极高的刻蚀选择比，因此，该湿法刻蚀方法可以对任意厚度的薄膜铌酸锂进行刻蚀(这是微纳加工工艺很难做到的)，从而实现大的刻蚀深度；该湿法刻蚀方法可以同时处理多个晶圆，且所涉及的所有的工艺都是CMOS兼容的，因此，这极大地提高了薄膜铌酸锂微纳加工的吞吐量并大大降低了成本。该湿法刻蚀方法的额外的优点将在下文中说明。As described above, the wet etching method has an extremely high etching selectivity ratio for thin-film lithium niobate, so the wet etching method can etch thin-film lithium niobate of any thickness (which is difficult to do in micro-nano processing), thereby achieving a large etching depth; the wet etching method can process multiple wafers at the same time, and all the processes involved are CMOS compatible, so this greatly improves the throughput of thin-film lithium niobate micro-nano processing and greatly reduces the cost. Additional advantages of the wet etching method will be described below.
在步骤(A)中，可以使用本领域中常用的多种切向的薄膜铌酸锂晶圆，例如x切向薄膜铌酸锂和z切向薄膜铌酸锂。优选地，该湿法刻蚀方法可以对z切向铌酸锂产生意外的刻蚀效果，这主要表现在所得铌酸锂脊状波导的侧壁性质和异常高的品质因子上。例如，本发明的湿法刻蚀方法所制得的x切向薄膜铌酸锂器件的本征品质因子可以达到1.85×10 6，而z切向薄膜铌酸锂器件的本征品质因子意外地可以达到1.21×10 7，这在本领域中可以超过现有的利用干法刻蚀获得的最优的薄膜铌酸锂器件的本征品质因子。 In step (A), various thin-film lithium niobate wafers commonly used in the art may be used, such as x-cut thin-film lithium niobate and z-cut thin-film lithium niobate. Preferably, the wet etching method can produce unexpected etching effects on z-cut lithium niobate, which is mainly manifested in the sidewall properties and abnormally high quality factor of the obtained lithium niobate ridge waveguide. For example, the intrinsic quality factor of the x-cut thin-film lithium niobate device prepared by the wet etching method of the present invention can reach 1.85×10 6 , while the intrinsic quality factor of the z-cut thin-film lithium niobate device can unexpectedly reach 1.21×10 7 , which can exceed the intrinsic quality factor of the best thin-film lithium niobate device obtained by dry etching in the art.
在步骤(B)中，可以利用本领域中常用的沉积方法，例如等离子体增强化学气相沉积(PECVD)形成二氧化硅薄层，并且，出于经济效益的考虑，二氧化硅薄层可以形成为纳米级薄层，例如厚度为50nm至200nm，优选为约100nm。In step (B), a silicon dioxide thin layer can be formed by a deposition method commonly used in the art, such as plasma enhanced chemical vapor deposition (PECVD), and for economic considerations, the silicon dioxide thin layer can be formed into a nanoscale thin layer, for example, with a thickness of 50 nm to 200 nm, preferably about 100 nm.
在本发明中，湿法刻蚀方法具有极高的刻蚀选择比，因此，所采用的二氧化硅掩模仅需要很薄的厚度，例如200nm以下，或100nm以下，或约50nm。因此，可以很方便的在二氧化硅掩模上加工出极窄(约50nm)的狭缝。在此，如果掩模过厚，对于窄的狭缝，二氧化硅掩模的深宽比会很大，用来刻蚀二氧化硅掩模的电子束胶的深宽比也会变大，这将导致加工工艺的困难性大大增加。因此，使用薄的二氧化硅掩模有利于在薄膜铌酸锂器件中得到波导之间的窄间距。In the present invention, the wet etching method has a very high etching selectivity, so the silicon dioxide mask used only needs a very thin thickness, for example, below 200nm, or below 100nm, or about 50nm. Therefore, it is very convenient to process an extremely narrow (about 50nm) slit on the silicon dioxide mask. Here, if the mask is too thick, for a narrow slit, the depth-to-width ratio of the silicon dioxide mask will be very large, and the depth-to-width ratio of the electron beam glue used to etch the silicon dioxide mask will also become larger, which will cause the difficulty of the processing technology to increase greatly. Therefore, using a thin silicon dioxide mask is conducive to obtaining a narrow spacing between waveguides in a thin-film lithium niobate device.
而且，湿法刻蚀利用溶液直接与铌酸锂薄膜发生化学反应，反应产物为溶于刻蚀液的物质。由于二氧化硅掩模比较薄，湿法刻蚀溶液与铌酸锂薄膜具有很好的浸润与交换，很方便对窄的狭缝进行刻蚀，同时也避免了干法刻蚀过程中存在的负载效应。Moreover, wet etching uses the solution to directly react chemically with the lithium niobate film, and the reaction product is a substance that dissolves in the etching solution. Since the silicon dioxide mask is relatively thin, the wet etching solution and the lithium niobate film have good wetting and exchange, which is very convenient for etching narrow slits, and also avoids the load effect that exists in the dry etching process.
接着，在步骤(C)中，可以利用本领域中已知的任何方法，形成光刻胶涂层，并进行曝光，将光刻胶涂层图案化。例如，首先可以用旋涂法将电子束胶形成在二氧化硅层上，然后用电子束曝光技术对电子束胶进行图案化，或者可以用与CMOS工艺兼容的光刻进行图案化。此处，电子束胶可以是ZEP 520A或者HSQ FOX16。Next, in step (C), a photoresist coating can be formed by any method known in the art, and then exposed to pattern the photoresist coating. For example, the electron beam glue can be first formed on the silicon dioxide layer by spin coating, and then patterned by electron beam exposure technology, or patterned by photolithography compatible with CMOS process. Here, the electron beam glue can be ZEP 520A or HSQ FOX16.
接着，在步骤(D)和(E)中，例如，可以利用电感耦合等离子体-反应离子刻蚀工艺，将电子束胶上的图案转移至二氧化硅层上，并除去残余的电子束胶。该过程可以如下进行，并且除去电子束胶的过程如下：Next, in steps (D) and (E), for example, the pattern on the electron beam glue can be transferred to the silicon dioxide layer using an inductively coupled plasma-reactive ion etching process, and the residual electron beam glue can be removed. The process can be performed as follows, and the process of removing the electron beam glue is as follows:
首先用电感耦合等离子体-反应离子刻蚀工艺对附着有图案化电子束胶的晶圆进行刻蚀。电子束胶覆盖的地方，二氧化硅被保留，电子束胶未覆盖的地方，二氧化硅被等离子体完全刻蚀掉，直至裸露出下面的铌酸锂薄膜层。然后将刻蚀后的晶圆放入去胶液(如二甲基甲酰胺)中，将残余的电子束胶(如ZEP 520A)去除。First, the wafer with patterned electron beam glue attached is etched using an inductively coupled plasma-reactive ion etching process. Silicon dioxide is retained where the electron beam glue is covered, and silicon dioxide is completely etched away by the plasma where the electron beam glue is not covered, until the lithium niobate film layer underneath is exposed. The etched wafer is then placed in a degumming solution (such as dimethylformamide) to remove the remaining electron beam glue (such as ZEP 520A).
进一步，在步骤(F)中，刻蚀液中H 2O 2、NH 4OH和H 2O的混合比为4:3:1至1:1:1，优选3:2:1至1:1:1，更优选为2:2:1。并且，刻蚀在60℃至90℃的范围下进行，优选在85℃进行。例如，刻蚀过程如下进行：利用二氧化硅做掩模，将薄膜铌酸锂浸泡在配比为2:2:1的H 2O 2、NH 4OH和H 2O的混合溶液中进行刻蚀，刻蚀温度为85℃。 Furthermore, in step (F), the mixing ratio of H 2 O 2 , NH 4 OH and H 2 O in the etching solution is 4:3:1 to 1:1:1, preferably 3:2:1 to 1:1:1, and more preferably 2:2:1. Moreover, the etching is performed at a temperature ranging from 60° C. to 90° C., preferably at 85° C. For example, the etching process is performed as follows: using silicon dioxide as a mask, the thin film lithium niobate is immersed in a mixed solution of H 2 O 2 , NH 4 OH and H 2 O in a ratio of 2:2:1 for etching, and the etching temperature is 85° C.
接着，在步骤(G)中，例如，通过氢氟酸缓冲溶液(BOE)去除二氧化硅掩模。然而，去除二氧化硅掩模的方法不限于此，可使用本领域中的常规方法。Next, in step (G), the silicon dioxide mask is removed by, for example, a hydrofluoric acid buffer solution (BOE). However, the method of removing the silicon dioxide mask is not limited thereto, and a conventional method in the art may be used.
最后，步骤(H)可以包括：将所得的薄膜铌酸锂器件在150℃至300℃的温度的气体环境如空气、氧气或氮气中退火1至4小时，优选在250℃的空气环境中退火2小时，从而修复晶体离子切割和湿法刻蚀过程中可能产生的缺陷，退火过程可有利于进一步提升所得铌酸锂薄膜器件的质量。Finally, step (H) may include: annealing the obtained thin film lithium niobate device in a gas environment such as air, oxygen or nitrogen at a temperature of 150°C to 300°C for 1 to 4 hours, preferably annealing in an air environment at 250°C for 2 hours, so as to repair defects that may be generated during the crystal ion cutting and wet etching process. The annealing process can help to further improve the quality of the obtained lithium niobate thin film device.
上述湿法刻蚀方法对x和z切向铌酸锂晶体的刻蚀速度均可高达约4nm/min以上。然而，刻蚀溶液对于二氧化硅掩模的刻蚀速率极低。这表明，该湿法刻蚀方法对铌酸锂晶体具有极高的刻蚀选择比。因此，该湿法刻蚀方法可以对任意厚度的薄膜铌酸锂进行刻蚀，而这是微纳加工工艺很难做到的。特别是，如上所述，该湿法刻蚀方法尤其适用于z切向铌酸锂晶体。The above wet etching method can achieve an etching rate of up to about 4 nm/min or more for both x- and z-tangent lithium niobate crystals. However, the etching rate of the etching solution for the silicon dioxide mask is extremely low. This indicates that the wet etching method has an extremely high etching selectivity for lithium niobate crystals. Therefore, the wet etching method can etch thin films of lithium niobate of any thickness, which is difficult to achieve with micro-nano processing. In particular, as described above, the wet etching method is particularly suitable for z-tangent lithium niobate crystals.
另一方面，本发明提供了由上述湿法刻蚀方法获得的薄膜铌酸锂器件。On the other hand, the present invention provides a thin film lithium niobate device obtained by the above wet etching method.
根据本发明，薄膜铌酸锂器件包含在z切向铌酸锂晶圆上刻蚀得到的脊状波导元件，其中，所述脊状波导元件包括直波导以及由波导构成的微环和/或微跑道，所述直波导与所述微环和/或微跑道相互构成耦合元件，并且所述脊状波导元件的侧立面的陡度为60°至70°之间，表面均方根粗糙度为0.5nm以下，构成耦合元件的直波导与微环和/或微跑道之间的最窄处的50nm至400nm。According to the present invention, a thin-film lithium niobate device comprises a ridge waveguide element etched on a z-tangent lithium niobate wafer, wherein the ridge waveguide element comprises a straight waveguide and a micro-ring and/or micro-track formed by the waveguide, the straight waveguide and the micro-ring and/or micro-track mutually constitute a coupling element, and the steepness of the side elevation of the ridge waveguide element is between 60° and 70°, the surface root mean square roughness is less than 0.5 nm, and the narrowest part between the straight waveguide and the micro-ring and/or micro-track constituting the coupling element is 50 nm to 400 nm.
图2示出了本发明的薄膜铌酸锂器件的基本结构的示意图，其中，图2(a)示出了薄膜铌酸锂器件包含直波导和微环的示意图，图2(b)示出了薄膜铌酸锂器件包含直波导和微跑道的示意图。在图2中，由长直线(部分弯曲)表示直波导，且由圆形或环形(封闭图形)表示微环或微跑道。FIG2 shows a schematic diagram of the basic structure of the thin film lithium niobate device of the present invention, wherein FIG2(a) shows a schematic diagram of the thin film lithium niobate device including a straight waveguide and a micro-ring, and FIG2(b) shows a schematic diagram of the thin film lithium niobate device including a straight waveguide and a micro-racetrack. In FIG2 , the straight waveguide is represented by a long straight line (partially curved), and the micro-ring or micro-racetrack is represented by a circle or annular shape (closed figure).
如图2所示，直波导和微环或微跑道之间存在耦合部(对应于图2中直线与环形相切的部分)，该耦合部对应于直波导与微环和/或微跑道之间的最窄处，且间距可低至50nm。根据器件要求，合适的间距范围例如为50nm至400nm，优选50nm至200nm。As shown in FIG2 , there is a coupling portion between the straight waveguide and the micro-ring or micro-track (corresponding to the portion where the straight line and the ring are tangent in FIG2 ), and the coupling portion corresponds to the narrowest part between the straight waveguide and the micro-ring and/or micro-track, and the spacing can be as low as 50 nm. According to the device requirements, the suitable spacing range is, for example, 50 nm to 400 nm, preferably 50 nm to 200 nm.
在此，对于z切向薄膜铌酸锂器件中的脊状波导而言，其具有相对垂直的侧壁，即陡度为60°至70°，这为高深宽比的狭缝的加工提供了基础，而在该湿法刻蚀的器件中，侧壁角度是制约狭缝深宽比的最关键的因素。通过此种陡度设置，可以实现高的狭缝深度，例如400nm以上，以及窄狭缝宽度，低至50nm。Here, for the ridge waveguide in the z-cut thin film lithium niobate device, it has a relatively vertical sidewall, that is, a steepness of 60° to 70°, which provides a basis for the processing of high aspect ratio slits, and in the wet etched device, the sidewall angle is the most critical factor restricting the aspect ratio of the slit. Through this steepness setting, a high slit depth, such as more than 400nm, and a narrow slit width, as low as 50nm, can be achieved.
在此，术语“陡度”是指波导的侧壁与基板之间的夹角(以锐角计)。Here, the term "steepness" refers to the angle (in terms of acute angle) between the sidewall of the waveguide and the substrate.
另外，所述脊状波导元件的侧立面的表面均方根粗糙度为0.5nm以下，这为提供优异的品质因子提供了良好的基础。表面均方根粗糙度优选小于0.5nm，如0.45nm以下，更优选0.4nm以下。另一方面，表面均方根粗糙度优选为0.1nm以上，更优选0.2nm以上。In addition, the surface root mean square roughness of the side elevation of the ridge waveguide element is less than 0.5 nm, which provides a good basis for providing an excellent quality factor. The surface root mean square roughness is preferably less than 0.5 nm, such as less than 0.45 nm, more preferably less than 0.4 nm. On the other hand, the surface root mean square roughness is preferably greater than 0.1 nm, more preferably greater than 0.2 nm.
虽然机理尚不明确，但据信上述陡度和表面均方根粗糙度的组合可以得到更高的品质因子，将光更好的束缚在所得到的波导元件中，并且能够得到具有高深宽比的狭缝。Although the mechanism is not yet clear, it is believed that the combination of steepness and surface RMS roughness can result in a higher quality factor, better confinement of light in the resulting waveguide element, and the ability to obtain slits with high aspect ratios.
本发明的薄膜铌酸锂器件的微环或微跑道具有非常高的品质因子，例如品质因子为10 6以上，对于x切向薄膜铌酸锂而言，品质因子可以高至1.85×10 6，特别是，意外的是，对于z切向薄膜铌酸锂而言，可以高至1.21×10 7。在本文中，品质因子是表征薄膜铌酸锂器件的微环或微跑道的本征品质因子。 The micro-ring or micro-track of the thin-film lithium niobate device of the present invention has a very high quality factor, for example, a quality factor of more than 10 6 , and for x-cut thin-film lithium niobate, the quality factor can be as high as 1.85×10 6 , and especially, surprisingly, for z-cut thin-film lithium niobate, it can be as high as 1.21×10 7. In this article, the quality factor is the intrinsic quality factor that characterizes the micro-ring or micro-track of the thin-film lithium niobate device.
本发明所制备的薄膜铌酸锂器件的优点在于，基于上述对高质量的波导和微环腔的湿法刻蚀的研究，可以对基于薄膜铌酸锂的电光调制器，声光调制器，热光调制器，非线性波长转换器件，电光频梳，克尔光频梳等光子学器件进行设计。这些器件在光通信、数据中心、传感(测距，光谱测量)、光量子信息处理等领域已经存在广泛应用。尤其是对于克尔光频梳，其色散工程往往需要比较厚的铌酸锂薄膜(大概1微米)，这对于ICP-RIE工艺是很难加工的，而湿法刻蚀可以很方便的对较厚的铌酸锂薄膜进行刻蚀。The advantage of the thin film lithium niobate device prepared by the present invention is that, based on the above-mentioned research on wet etching of high-quality waveguides and micro-ring cavities, electro-optic modulators, acousto-optic modulators, thermo-optic modulators, nonlinear wavelength conversion devices, electro-optic frequency combs, Kerr optical frequency combs and other photonic devices based on thin film lithium niobate can be designed. These devices have been widely used in the fields of optical communication, data centers, sensing (ranging, spectral measurement), and optical quantum information processing. In particular, for the Kerr optical frequency comb, its dispersion engineering often requires a relatively thick lithium niobate film (about 1 micron), which is difficult to process for the ICP-RIE process, while wet etching can easily etch the thicker lithium niobate film.
实施例Example
下文将参考实施例更详细地描述本发明。Hereinafter, the present invention will be described in more detail with reference to Examples.
然而，以下的实施例和比较例仅用于说明本发明，而本发明的内容不限于下文所述的实施例和比较例。However, the following Examples and Comparative Examples are only for illustrating the present invention, and the contents of the present invention are not limited to the Examples and Comparative Examples described below.
实施例中涉及的原料和设备的来源披露如下：The sources of the raw materials and equipment involved in the examples are disclosed as follows:
薄膜铌酸锂晶片：济南晶正科技Thin-film lithium niobate wafer: Jinan Jingzheng Technology
刻蚀液：H 2O 2、NH 4OH和H 2O市售试剂，配制为2:2:1的混合溶液 Etching solution: H 2 O 2 , NH 4 OH and H 2 O commercial reagents, prepared as a 2:2:1 mixed solution
等离子体增强化学气相沉积设备：System100,OxfordPlasma enhanced chemical vapor deposition equipment: System100, Oxford
电子束曝光设备：EBPG 5000plus,VistecElectron beam lithography equipment: EBPG 5000plus, Vistec
电子束胶：ZEP 520A,ZeonElectron beam glue: ZEP 520A, Zeon
电感耦合等离子体-反应离子设备：SI 500,SentechInductively coupled plasma-reactive ion equipment: SI 500, Sentech
退火设备：RTH-4，济南创谱仪器Annealing equipment: RTH-4, Jinan Chuangpu Instruments
光谱扫描设备：实验室搭建的光谱扫描***，主要包括一台可调谐激光器(TSL 550，Santec),一台三桨偏振控制器(FPC560,Thorlabs)，三个三轴位移台(两台MAX303/M和一台RB13M/M，Thorlabs)和一台光电探测器(PDA10CS2,Thorlabs)Spectral scanning equipment: The spectral scanning system built in the laboratory mainly includes a tunable laser (TSL 550, Santec), a three-paddle polarization controller (FPC560, Thorlabs), three three-axis translation stages (two MAX303/M and one RB13M/M, Thorlabs) and a photodetector (PDA10CS2, Thorlabs)
扫描电镜设备：SU8220,HitachiScanning electron microscope equipment: SU8220, Hitachi
原子力显微镜：Dimension FastScan,BrukerAtomic force microscope: Dimension FastScan, Bruker
实施例1Example 1
湿法刻蚀的第一步是在薄膜铌酸锂晶片(x切向)上用等离子体增强化学气相沉积工艺沉积一层100nm厚的二氧化硅。然后，用电子束曝光工艺将图案写在旋涂在二氧化硅上面的电子束胶上。接着，通过电感耦合等离子体-反应离子刻蚀工艺，将电子束胶上的图案转移至二氧化硅层上，并除去残余的电子束胶。然后，利用二氧化硅做掩模，将薄膜铌酸锂浸泡在配比为2:2:1的H 2O 2、NH 4OH和H 2O的混合溶液中进行刻蚀，刻蚀温度为85℃。湿法刻蚀结束后，利用氢氟酸缓冲溶液(BOE)去除二氧化硅掩模。接着，样品在250℃的空气环境中退火2小时，用来修复晶体离子切割和湿法刻蚀过程中可能产生的缺陷。最后，样品的端面被划开，用来进行后面的光纤和样品之间的耦合。湿法刻蚀的速度为4nm/min。 The first step of wet etching is to deposit a 100nm thick layer of silicon dioxide on the thin-film lithium niobate wafer (x-cut) using a plasma-enhanced chemical vapor deposition process. Then, the pattern is written on the electron beam glue spun on the silicon dioxide using an electron beam exposure process. Then, the pattern on the electron beam glue is transferred to the silicon dioxide layer by an inductively coupled plasma-reactive ion etching process, and the residual electron beam glue is removed. Then, using silicon dioxide as a mask, the thin-film lithium niobate is immersed in a mixed solution of H 2 O 2 , NH 4 OH and H 2 O with a ratio of 2:2:1 for etching, and the etching temperature is 85°C. After the wet etching is completed, the silicon dioxide mask is removed using a hydrofluoric acid buffer solution (BOE). Then, the sample is annealed in an air environment at 250°C for 2 hours to repair the defects that may be generated during the crystal ion cutting and wet etching process. Finally, the end face of the sample is cut open for the coupling between the optical fiber and the sample later. The wet etching speed is 4nm/min.
另外，在本实施例中，利用上述湿法刻蚀工艺加工了直波导和微环。薄膜铌酸锂的厚度是600nm，刻蚀深度是300nm。x切向薄膜铌酸锂的微环半径为120μm。为了减少传输损失，微环中波导的顶部宽度为2.6μm，耦合波导的顶部宽度被设计为1.4μm。In addition, in this embodiment, the straight waveguide and micro-ring are processed by the above-mentioned wet etching process. The thickness of the thin-film lithium niobate is 600nm, and the etching depth is 300nm. The radius of the micro-ring of the x-cut thin-film lithium niobate is 120μm. In order to reduce transmission loss, the top width of the waveguide in the micro-ring is 2.6μm, and the top width of the coupled waveguide is designed to be 1.4μm.
实施例2Example 2
通过与实施例1中描述相同的方法对薄膜铌酸锂晶片进行湿法刻蚀，不同之处在于，薄膜铌酸锂晶片是z切向的。湿法刻蚀的速度也为4nm/min。The thin film lithium niobate wafer was wet etched by the same method as described in Example 1, except that the thin film lithium niobate wafer was z-tangential. The wet etching rate was also 4 nm/min.
在本实施例中，利用上述湿法刻蚀工艺加工了直波导和微跑道。薄膜铌酸锂的厚度是600nm，刻蚀深度是300nm。z切向薄膜铌酸锂的微跑道半径为120μm，微跑道的直线部分的长度为3000μm。为了减少传输损失，耦合波导的顶部宽度为1.6μm，微跑道中波导的顶部宽度为4μm。In this embodiment, the straight waveguide and micro-track were processed by the above-mentioned wet etching process. The thickness of the thin film lithium niobate is 600nm, and the etching depth is 300nm. The radius of the micro-track of the z-tangential thin film lithium niobate is 120μm, and the length of the straight part of the micro-track is 3000μm. In order to reduce transmission loss, the top width of the coupled waveguide is 1.6μm, and the top width of the waveguide in the micro-track is 4μm.
比较例1Comparative Example 1
利用RIE刻蚀加CMP抛光工艺，在z切向铌酸锂薄膜(来自于济南晶正(NanoLN)公司)上进行干法蚀刻工艺，具体参数为，铌酸锂薄膜的厚度为700nm，微环中波导的宽度为7μm(数据来自Wolf R,Breunig I,Zappe H,et al.Cascaded second-order optical nonlinearities in on-chip micro rings[J].Optics express,2017,25(24):29927-29933.)。The dry etching process was performed on the z-cut lithium niobate film (from Jinan NanoLN Company) using RIE etching and CMP polishing process. The specific parameters are: the thickness of the lithium niobate film is 700nm, and the width of the waveguide in the microring is 7μm (data from Wolf R, Breunig I, Zappe H, et al. Cascaded second-order optical nonlinearities in on-chip micro rings [J]. Optics express, 2017, 25(24): 29927-29933.).
比较例2Comparative Example 2
利用ICP-RIE技术(ICP-RIE属于干法刻蚀的一种)，对x切向铌酸锂薄膜(来自于济南晶正(NanoLN)公司)进行刻蚀。具体参数为，铌酸锂薄膜的厚度600nm，刻蚀深度350nm，微跑道中波导的宽度为2.4μm(数据来自Zhang M,Wang C,Cheng R,et al.Monolithic ultra-high-Q lithium niobate microring resonator[J].Optica,2017,4(12):1536-1537.)。The x-cut lithium niobate film (from Jinan NanoLN Company) was etched using ICP-RIE technology (ICP-RIE is a type of dry etching). The specific parameters are: the thickness of the lithium niobate film is 600nm, the etching depth is 350nm, and the width of the waveguide in the microtrack is 2.4μm (data from Zhang M, Wang C, Cheng R, et al. Monolithic ultra-high-Q lithium niobate microring resonator [J]. Optica, 2017, 4 (12): 1536-1537.).
比较例3Comparative Example 3
利用CMP技术，对x切向铌酸锂薄膜(来自于济南晶正(NanoLN)公司)进行刻蚀。具体参数为，铌酸锂薄膜的厚度400nm，加工的深度400nm，微环中波导的宽度为3μm(数据来自Wu R,Wang M,Xu J,et al.Long low-loss-lithium niobate on insulator waveguides with sub-nanometer surface roughness[J].Nanomaterials,2018,8(11):910.)。The x-cut lithium niobate film (from Jinan NanoLN) was etched using CMP technology. The specific parameters are: the thickness of the lithium niobate film is 400nm, the processing depth is 400nm, and the width of the waveguide in the microring is 3μm (data from Wu R, Wang M, Xu J, et al. Long low-loss-lithium niobate on insulator waveguides with sub-nanometer surface roughness [J]. Nanomaterials, 2018, 8 (11): 910.).
该CMP法刻蚀不能形成直波导和微环之间的窄狭缝(50nm)。The CMP etching method cannot form a straight waveguide and a narrow gap (50 nm) between the microrings.
实验例1：品质因子的测定Experimental Example 1: Determination of Quality Factor
通过光谱扫描，对实施例1和2中获得的x和z切向薄膜铌酸锂上的微环和微跑道的品质因子进行测量。如图3(a)所示，实施例1的x切向薄膜铌酸锂上的微环的TE 0模式的加载品质因子最高达1.05×10 6，其归一化的透射峰的最小值为0.019。因此，对应的本征品质因子为1.85×10 6。 By spectral scanning, the quality factors of the micro-rings and micro-tracks on the x- and z-tangential thin-film lithium niobate obtained in Examples 1 and 2 were measured. As shown in Figure 3(a), the loading quality factor of the TE 0 mode of the micro-rings on the x-tangential thin-film lithium niobate of Example 1 is up to 1.05×10 6 , and the minimum value of its normalized transmission peak is 0.019. Therefore, the corresponding intrinsic quality factor is 1.85×10 6 .
如图3(b)所示，实施例2的z切向薄膜铌酸锂上的微跑道的TE 0模式的加载品质因子最高达8.03×10 6，其归一化的透射峰的最小值为0.1058。因此，对应的本征品质因子为1.21×10 7。 As shown in FIG3( b ), the loading quality factor of the TE 0 mode of the micro-track on the z-cut thin film lithium niobate of Example 2 is up to 8.03×10 6 , and the minimum value of its normalized transmission peak is 0.1058. Therefore, the corresponding intrinsic quality factor is 1.21×10 7 .
由此可见，z切向薄膜铌酸锂上的波导的形状更规则，且其品质因子高于x切向薄膜铌酸锂上的微环的品质因子。上述结果证明了湿法刻蚀可以实现高质量的基于薄膜铌酸锂的光子结构。It can be seen that the shape of the waveguide on the z-cut thin-film lithium niobate is more regular, and its quality factor is higher than the quality factor of the microring on the x-cut thin-film lithium niobate. The above results prove that wet etching can achieve high-quality photonic structures based on thin-film lithium niobate.
另外，比较例1中对于z切向薄膜铌酸锂，实现了3×10 6的微环的品质因子；比较例2中对于x切向薄膜铌酸锂，实现了1×10 7的微环的本征品质因子；比较例3中对于x切向薄膜铌酸锂，实现了1.14×10 7的微环的本征品质因子，这是本领域中迄今为止最高的微环的品质因子。 In addition, in Comparative Example 1, for the z-tangent thin film lithium niobate, a quality factor of the microring of 3×10 6 was achieved; in Comparative Example 2, for the x-tangent thin film lithium niobate, an intrinsic quality factor of the microring of 1×10 7 was achieved; in Comparative Example 3, for the x-tangent thin film lithium niobate, an intrinsic quality factor of the microring of 1.14×10 7 was achieved, which is the highest quality factor of the microring in this field to date.
由此可见，本发明用湿法刻蚀方法获得的薄膜铌酸锂器件的品质因子与本领域中采用干法蚀刻获得薄膜铌酸锂器件的品质因子是相仿的；特别地，对于z切向薄膜铌酸锂器件而言，本发明(实施例2)的品质因子甚至高于干法蚀刻获得的z切向薄膜铌酸锂器件的品质因子以及本领域迄今为止在x切向薄膜铌酸锂中获得的最高品质因子。这一点对于薄膜铌酸锂的加工而言尤其重要，因为采用本发明的湿法刻蚀方法工艺简单、成本低廉，可以方便且大批量地生产具有高品质因子的薄膜铌酸锂器件。It can be seen that the quality factor of the thin-film lithium niobate device obtained by the wet etching method of the present invention is similar to the quality factor of the thin-film lithium niobate device obtained by dry etching in the art; in particular, for the z-tangent thin-film lithium niobate device, the quality factor of the present invention (Example 2) is even higher than the quality factor of the z-tangent thin-film lithium niobate device obtained by dry etching and the highest quality factor obtained in the x-tangent thin-film lithium niobate in the art so far. This is particularly important for the processing of thin-film lithium niobate, because the wet etching method of the present invention is simple in process and low in cost, and thin-film lithium niobate devices with high quality factors can be produced conveniently and in large quantities.
实验例2：波导的扫描电镜(SEM)图像分析Experimental Example 2: SEM Image Analysis of Waveguide
对实施例1和2所得x-和z切向薄膜铌酸锂上的脊状波导进行SEM分析。图4示出了实验结果，其中，图4(a)和(b)是实施例1的x切向薄膜铌酸锂上的脊状波导在y和z轴方向上的横截面；而图4(c)和(d)实施例2的z切向薄膜铌酸锂上的脊状波导在y和x轴方向上的横截面。SEM analysis was performed on the ridge waveguides on the x- and z-tangential thin-film lithium niobate obtained in Examples 1 and 2. Figure 4 shows the experimental results, wherein Figures 4(a) and (b) are cross-sections of the ridge waveguide on the x-tangential thin-film lithium niobate of Example 1 in the y and z-axis directions; and Figures 4(c) and (d) are cross-sections of the ridge waveguide on the z-tangential thin-film lithium niobate of Example 2 in the y and x-axis directions.
由图4可以看出，铌酸锂的x，y和z三个主轴上的湿法刻蚀特性是非常不同的。甚至是对于某个选定的主轴方向，其正方向和负方向上的湿法刻蚀特性也是不同的。其中，±z方向上的湿法刻蚀特性的不同是最强的(图4(a))。相比之下，±y方向上湿法刻蚀特性的不同相对较小(图4(b)和(d))，而±x方向上的湿法刻蚀特性是相同的(图4(c))。除此之外，对于x切向薄膜铌酸锂上加工出的波导，其±y方向和-z方向的侧壁边缘是曲线，﹢z方向的侧壁比较垂直，角度为85°(图4(a)和(b))，而且，x切向薄膜铌酸锂中存在更强的横向刻蚀问题。对于z切向薄膜铌酸锂上加工出的波导，所有侧壁的边缘均为直线。其中，±x和﹢y方向的侧壁的角度约为60°，-y方向侧壁的角度约为70°(图4(c)和(d))。As can be seen from Figure 4, the wet etching characteristics of lithium niobate in the three main axes of x, y and z are very different. Even for a selected main axis direction, the wet etching characteristics in the positive and negative directions are different. Among them, the difference in wet etching characteristics in the ±z direction is the strongest (Figure 4(a)). In contrast, the difference in wet etching characteristics in the ±y direction is relatively small (Figures 4(b) and (d)), while the wet etching characteristics in the ±x direction are the same (Figure 4(c)). In addition, for the waveguide processed on the x-cut thin film lithium niobate, the sidewall edges in the ±y direction and -z direction are curved, and the sidewalls in the +z direction are relatively vertical with an angle of 85° (Figures 4(a) and (b)). Moreover, there is a stronger lateral etching problem in the x-cut thin film lithium niobate. For the waveguide processed on the z-cut thin film lithium niobate, the edges of all sidewalls are straight lines. The angles of the side walls in the ±x and +y directions are approximately 60°, and the angle of the side walls in the -y direction is approximately 70° (Fig. 4(c) and (d)).
实验例3：直波导和微环/微跑道之间的狭缝的评价Experimental Example 3: Evaluation of the Slit between the Straight Waveguide and the Micro-Ring/Micro-Racetrack
对实施例1和2中形成的薄膜铌酸锂器件中直波导和微环/微跑道之间的狭缝进行了观察和评价。利用SEM获得了其显微图像。对狭缝的宽度进行了测量，发现实施例2 的z切向薄膜铌酸锂中形成了较窄的约50nm的狭缝，而x切向薄膜铌酸锂中的狭缝由于湿法刻蚀过程中存在更大的横向刻蚀，其狭缝宽度明显较宽。图5示出了实施例2的z切向薄膜铌酸锂中形成的狭缝的SEM图。The slits between the straight waveguide and the micro-ring/micro-racetrack in the thin-film lithium niobate devices formed in Examples 1 and 2 were observed and evaluated. Microscopic images thereof were obtained using SEM. The width of the slits was measured, and it was found that a narrower slit of about 50 nm was formed in the z-tangential thin-film lithium niobate of Example 2, while the slits in the x-tangential thin-film lithium niobate were significantly wider due to the greater lateral etching during the wet etching process. FIG5 shows an SEM image of the slits formed in the z-tangential thin-film lithium niobate of Example 2.
关于比较例3，由于CMP磨抛出来的波导侧壁陡度一般比较小，因此需要比较大的刻蚀深度，才能将光更好的束缚住。同时，由于CMP磨抛出来的波导侧壁陡度较小，据信比较例3中并不能形成窄狭缝。Regarding Comparative Example 3, since the steepness of the waveguide sidewall polished by CMP is generally relatively small, a relatively large etching depth is required to better confine the light. At the same time, since the steepness of the waveguide sidewall polished by CMP is relatively small, it is believed that a narrow slit cannot be formed in Comparative Example 3.
另外，如上所述，由于波导的侧壁形态良好，可以预期形成200nm以上、例如400nm以上的狭缝深度。In addition, as described above, since the side wall morphology of the waveguide is good, it is expected that the slit depth can be formed to be greater than 200 nm, for example, greater than 400 nm.
实验例4：波导的表面均方根粗糙度的评价Experimental Example 4: Evaluation of the Surface RMS Roughness of Waveguide
对实施例1和2中形成的薄膜铌酸锂器件中的波导进行了表面粗糙度测试。利用原子力显微镜(Dimension FastScan,Bruker)对样片表面进行测试，工作模式为峰值力敲击模式(peakforce tapping mode)。在获得的数据中，取均方根粗糙度和相干长度来表征薄膜铌酸锂器件中的波导的表面粗糙情况，由此获得的实验结果如下表1所示。The surface roughness of the waveguide in the thin-film lithium niobate device formed in Examples 1 and 2 was tested. The surface of the sample was tested using an atomic force microscope (Dimension FastScan, Bruker), and the working mode was peak force tapping mode. In the obtained data, the root mean square roughness and coherence length were used to characterize the surface roughness of the waveguide in the thin-film lithium niobate device. The experimental results obtained are shown in Table 1 below.
表1.实施例1和2的薄膜铌酸锂的表面均方根粗糙度的测量结果。Table 1. Measurement results of the surface root mean square roughness of the thin film lithium niobate of Examples 1 and 2.
Figure PCTCN2022128685-appb-000001
Figure PCTCN2022128685-appb-000001
由表1可见，湿法刻蚀后薄膜铌酸锂(波导侧壁)的表面均方根粗糙度并没有增大很多，均保持低于0.5nm，这样的表面粗糙度保持了良好的品质因子(如以上实验例1所测得)，并且与上述波导侧壁的陡度一起为得到具有高深宽比的狭缝提供了良好的基础。As can be seen from Table 1, the surface RMS roughness of the thin film lithium niobate (waveguide side wall) after wet etching does not increase much, and remains below 0.5 nm. Such surface roughness maintains a good quality factor (as measured in Experimental Example 1 above), and together with the steepness of the waveguide side wall, provides a good basis for obtaining a slit with a high aspect ratio.
在前述说明书和相关附图中存在的教导的帮助下，本领域技术人员将意识到本文所述技术方案的多种变形和其它实施方式。因此，将理解的是，本发明不限于所公开的特定实施方式，且任何变形和其它实施方式均视为包括在所附权利要求书的范围内。With the help of the teachings in the foregoing description and the related drawings, those skilled in the art will recognize various variations and other embodiments of the technical solutions described herein. Therefore, it will be understood that the present invention is not limited to the specific embodiments disclosed, and any variations and other embodiments are deemed to be included within the scope of the appended claims.

Claims (15)

  1. 一种薄膜铌酸锂的湿法刻蚀方法，所述方法包括利用包含H 2O 2、NH 4OH和H 2O的混合溶液作为刻蚀液对薄膜铌酸锂晶圆进行刻蚀，其特征在于，所述方法包括以下步骤： A wet etching method for thin-film lithium niobate, the method comprising etching a thin-film lithium niobate wafer using a mixed solution comprising H 2 O 2 , NH 4 OH and H 2 O as an etching solution, characterized in that the method comprises the following steps:
    (1)在薄膜铌酸锂晶圆的一个表面上沉积二氧化硅薄层；(1) depositing a thin layer of silicon dioxide on one surface of a thin-film lithium niobate wafer;
    (2)将二氧化硅薄层图案化；(2) patterning the silicon dioxide thin layer;
    (3)利用图案化的二氧化硅薄层作为掩模，将薄膜铌酸锂晶圆浸入作为刻蚀液的H 2O 2、NH 4OH和H 2O的混合溶液中进行刻蚀； (3) using the patterned silicon dioxide thin layer as a mask, immersing the thin film lithium niobate wafer in a mixed solution of H 2 O 2 , NH 4 OH and H 2 O as an etching solution for etching;
    (4)去除二氧化硅薄层，由此得到本发明的薄膜铌酸锂器件，(4) removing the silicon dioxide thin layer, thereby obtaining the thin film lithium niobate device of the present invention,
    其中，所述薄膜铌酸锂晶圆是z切向薄膜铌酸锂晶圆。Wherein, the thin film lithium niobate wafer is a z-tangential thin film lithium niobate wafer.
  2. 如权利要求1所述的方法，其中，步骤(1)中的二氧化硅薄层的厚度为50nm至200nm。The method according to claim 1, wherein the thickness of the silicon dioxide thin layer in step (1) is 50 nm to 200 nm.
  3. 如权利要求1所述的方法，其中，步骤(4)中的刻蚀在60℃至90℃的范围下进行。The method according to claim 1, wherein the etching in step (4) is performed at a temperature in the range of 60°C to 90°C.
  4. 如权利要求1所述的方法，其还包括：将所得的薄膜铌酸锂器件在150℃至300℃的温度的气体环境中退火1至4小时，该气体包括空气、氧气或氮气。The method according to claim 1 further comprises: annealing the obtained thin film lithium niobate device in a gas environment at a temperature of 150° C. to 300° C. for 1 to 4 hours, the gas comprising air, oxygen or nitrogen.
  5. 如权利要求1所述的方法，其中，步骤(4)中的刻蚀速度是2nm/min以上。The method according to claim 1, wherein the etching rate in step (4) is greater than 2 nm/min.
  6. 如权利要求1所述的方法，其中，所述铌酸锂晶圆上的铌酸锂层的刻蚀深度为200nm以上。The method according to claim 1, wherein the etching depth of the lithium niobate layer on the lithium niobate wafer is greater than 200 nm.
  7. 如权利要求1所述的方法，其中，步骤(2)包括在二氧化硅薄层上形成50nm至400nm之间的狭缝。The method of claim 1, wherein step (2) comprises forming a slit between 50 nm and 400 nm in the silicon dioxide thin layer.
  8. 一种薄膜铌酸锂器件，其由权利要求1至7中任一项所述的湿法刻蚀方法获得。A thin film lithium niobate device is obtained by the wet etching method according to any one of claims 1 to 7.
  9. 如权利要求8所述的薄膜铌酸锂器件，其包括脊状波导元件，所述脊状波导元件的侧立面的陡度为60°至70°之间，表面均方根粗糙度为0.5nm以下。The thin film lithium niobate device as claimed in claim 8, comprising a ridge waveguide element, wherein the steepness of the side elevation of the ridge waveguide element is between 60° and 70°, and the surface root mean square roughness is less than 0.5 nm.
  10. 如权利要求9所述的薄膜铌酸锂器件，其中，相邻的脊状波导元件之间最窄处的间距为50nm至400nm。The thin film lithium niobate device as claimed in claim 9, wherein the narrowest distance between adjacent ridge waveguide elements is 50 nm to 400 nm.
  11. 如权利要求8所述的薄膜铌酸锂器件，其中，脊状波导元件包括直波导以及微环和/或微跑道。The thin film lithium niobate device as claimed in claim 8, wherein the ridge waveguide element comprises a straight waveguide and a micro-ring and/or a micro-racetrack.
  12. 如权利要求11所述的薄膜铌酸锂器件，其中，所述直波导与所述微环和/或微跑道相互构成耦合元件，且构成耦合元件的直波导与微环和/或微跑道之间的最窄处的深度为200nm以上。The thin film lithium niobate device as described in claim 11, wherein the straight waveguide and the micro-ring and/or micro-track constitute a coupling element with each other, and the narrowest depth between the straight waveguide and the micro-ring and/or micro-track constituting the coupling element is greater than 200 nm.
  13. 一种薄膜铌酸锂器件，其包含在z切向铌酸锂晶圆上刻蚀得到的脊状波导元件，其中，所述脊状波导元件包括直波导以及由波导构成的微环和/或微跑道，所述直波导与所述微环和/或微跑道相互构成耦合元件，并且所述脊状波导元件的侧立面的陡度为60°至70°之间，表面均方根粗糙度为0.5nm以下，构成耦合元件的直波导与微环和/或微跑道之间的最窄处的间距为50nm至400nm。A thin film lithium niobate device comprises a ridge waveguide element etched on a z-tangent lithium niobate wafer, wherein the ridge waveguide element comprises a straight waveguide and a micro-ring and/or micro-track formed by the waveguide, the straight waveguide and the micro-ring and/or micro-track mutually constitute a coupling element, and the steepness of the side elevation of the ridge waveguide element is between 60° and 70°, the surface root mean square roughness is below 0.5nm, and the narrowest distance between the straight waveguide and the micro-ring and/or micro-track constituting the coupling element is between 50nm and 400nm.
  14. 如权利要求13所述的薄膜铌酸锂器件，其中，直波导与微环和/或微跑道之间的最窄处的深度为200nm以上。The thin film lithium niobate device as claimed in claim 13, wherein the depth of the narrowest part between the straight waveguide and the micro-ring and/or micro-racetrack is greater than 200 nm.
  15. 如权利要求13所述的薄膜铌酸锂器件，其品质因子为1×10 6至1.21×10 7。 The thin film lithium niobate device according to claim 13, wherein the quality factor is 1×10 6 to 1.21×10 7 .
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US6195191B1 (en) * 1999-08-19 2001-02-27 Lucent Technologies, Inc. Optical devices having improved temperature stability
CN110764188A (en) * 2019-10-23 2020-02-07 天津大学 Preparation method of lithium niobate ridge type optical waveguide
CN111505767A (en) * 2020-04-28 2020-08-07 上海交通大学 Preparation method of lithium niobate photonic chip based on silicon oxide mask
CN112596160A (en) * 2020-12-16 2021-04-02 南京中电芯谷高频器件产业技术研究院有限公司 Preparation method of high-quality thin-film lithium niobate micro-nano grating

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Publication number Priority date Publication date Assignee Title
US6195191B1 (en) * 1999-08-19 2001-02-27 Lucent Technologies, Inc. Optical devices having improved temperature stability
CN110764188A (en) * 2019-10-23 2020-02-07 天津大学 Preparation method of lithium niobate ridge type optical waveguide
CN111505767A (en) * 2020-04-28 2020-08-07 上海交通大学 Preparation method of lithium niobate photonic chip based on silicon oxide mask
CN112596160A (en) * 2020-12-16 2021-04-02 南京中电芯谷高频器件产业技术研究院有限公司 Preparation method of high-quality thin-film lithium niobate micro-nano grating

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