A method for preparing a low-loss thin-film lithium niobate optical waveguide based on electron beam resist
By using electron beam photoresist and pure argon etching, the problems of low processing precision and high loss in thin-film lithium niobate optical waveguides were solved, achieving high-precision, low-loss fabrication of thin-film lithium niobate optical waveguides and simplifying the process flow.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUAZHONG UNIV OF SCI & TECH
- Filing Date
- 2023-03-24
- Publication Date
- 2026-07-31
AI Technical Summary
Existing technologies for fabricating thin-film lithium niobate optical waveguides suffer from problems such as low processing accuracy, high loss, and complex process steps. In particular, the lithium fluoride byproducts caused by the hard mask etching method increase the roughness and loss of the waveguide sidewalls.
Electron beam photoresist was used as a mask, combined with inductively coupled plasma etching, and pure argon gas was used for etching to avoid the growth of hard masks. The photoresist mask layer was directly prepared on the thin film lithium niobate, and a low-loss thin film lithium niobate optical waveguide was formed through a precise etching process.
A thin-film lithium niobate optical waveguide with high processing precision and low loss has been achieved, simplifying the process steps, reducing waveguide sidewall roughness and transmission loss, and improving device integration and performance.
Smart Images
Figure CN116338857B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of thin-film lithium niobate optical waveguides, and more particularly to a method for fabricating low-loss thin-film lithium niobate optical waveguides based on electron beam photoresist. Background Technology
[0002] Lithium niobate is a multifunctional material with electro-optic effects, nonlinear optics, piezoelectricity, and ferroelectricity, and it has been widely used in optical communication and integrated optoelectronic devices. Compared to bulk lithium niobate, thin-film lithium niobate possesses both excellent electro-optic properties and on-chip integration capabilities, gradually becoming a potential solution for next-generation photonic integrated devices. The development of modulators, optical microcavities, mode converters, and other devices based on the thin-film lithium niobate platform offers possibilities for addressing current optical communication and signal processing needs. To realize optoelectronic devices based on thin-film lithium niobate, various integrated optical waveguide structures need to be designed. Achieving high-precision, low-loss optical waveguide structures through fabrication processes is of great significance for the fabrication of large-scale thin-film lithium niobate optoelectronic devices and for effectively improving device performance.
[0003] However, fabricating low-loss thin-film lithium niobate waveguides remains an international challenge. Fabricating waveguides on thin-film lithium niobate wafers using photolithography and etching processes has been a research hotspot in recent years. Traditional methods for fabricating thin-film lithium niobate waveguides involve etching the thin film using hard masks such as metal or silicon dioxide. For example, patents CN114755761A and CN110764185A use metal hard masks for etching. Because this method uses fluorine-based gases, byproducts such as lithium fluoride inevitably adhere to the waveguide surface during etching, increasing the roughness of the waveguide sidewalls and thus increasing transmission loss. Furthermore, hard masks reduce the dimensional accuracy of the waveguide fabrication, hindering fine processing. In addition, growing hard masks increases the number of steps in the waveguide fabrication process, raising its complexity.
[0004] The fabrication accuracy and transmission loss of waveguides have a significant impact on the performance of optoelectronic devices based on thin-film lithium niobate platforms. Therefore, it is necessary to explore a new process fabrication scheme to achieve high fabrication accuracy and low loss in thin-film lithium niobate optical waveguides. Summary of the Invention
[0005] In view of this, the present invention proposes a method for fabricating low-loss thin-film lithium niobate optical waveguides based on electron beam photoresist. This method has the advantages of high processing accuracy, while avoiding the growth of hard masks to simplify the processing flow and avoiding the generation of lithium fluoride byproducts, thus effectively reducing waveguide loss.
[0006] The technical solution of this invention is achieved as follows: This invention provides a method for fabricating low-loss thin-film lithium niobate optical waveguides based on electron beam photoresist, comprising the following steps:
[0007] S1, a pre-prepared thin-film lithium niobate wafer is provided as a substrate, wherein the thin-film lithium niobate wafer comprises, from bottom to top, a silicon substrate layer, a silicon dioxide layer and a thin-film lithium niobate layer;
[0008] S2, spin-coating electron beam photoresist onto the surface of the thin film lithium niobate layer, and pre-baking the photoresist;
[0009] S3, the mask pattern is transferred onto the photoresist using electron beam exposure after drying, and the sample is then post-baked;
[0010] S4, the dried photoresist is sequentially developed and fixed to form a photoresist mask layer, and then the thin film lithium niobate layer is etched by inductively coupled plasma etching process to transfer the pattern on the photoresist to the thin film lithium niobate layer. The etching gas is argon.
[0011] S5, remove the residual photoresist on the thin-film lithium niobate layer to obtain a low-loss thin-film lithium niobate optical waveguide.
[0012] In step S2, the electron beam photoresist used is AR-P6200.13, the spin coating speed is 2000-3000 r / min, and the spin coating time is 1-2 min.
[0013] Based on the above technical solution, preferably, in step S2, the thin film lithium niobate wafer needs to be cleaned before spin-coating electron beam photoresist. The cleaning method is as follows: first, place the thin film lithium niobate sample in acetone and sonicate for 5-10 minutes, then place it in isopropanol solution and sonicate for 5-10 minutes, and then rinse it in deionized water for 10-15 seconds.
[0014] Based on the above technical solutions, preferably, the pre-baking and post-baking methods in steps S2 and S3 are as follows: place the sample on a heating plate and bake it at 130-150℃ for 1-2 minutes.
[0015] Based on the above technical solution, preferably, in step S4 etching process, the argon gas flow rate is 30-50 sccm, the radio frequency power is 100-150W, the ICP power is 600-800W, the etching selectivity ratio of lithium niobate to photoresist is (1-1.3):1, and the etching rate of lithium niobate is about 30-50 nm / min; after etching for 8-12 min, the pattern of the photoresist mask layer is transferred to the lithium niobate layer to form a ridge-shaped thin film lithium niobate optical waveguide with an etching depth of 350-370 nm.
[0016] Based on the above technical solutions, preferably, the method for removing residual photoresist in step S5 is as follows: immerse the sample in a photoresist remover solution for 1-3 hours to dissolve the remaining photoresist, and then take out the sample and rinse it under deionized water for 10-30 seconds; the photoresist remover solution is N-methylpyrrolidone or acetone.
[0017] Based on the above technical solution, preferably, after removing the residual photoresist in step S5, it is also necessary to remove the residual organic byproducts. The method is as follows: place the sample in the cleaning solution and heat it in a water bath at 60℃-80℃ for 30-60 minutes to dissolve the residual organic matter on the lithium niobate layer. Then, take out the sample and rinse it in deionized water for 10-30 seconds to finally obtain the thin film lithium niobate optical waveguide. The cleaning solution is prepared by ammonia water: hydrogen peroxide: deionized water in a volume ratio of (1-2):(1-3):5.
[0018] Based on the above technical solutions, preferably, the lithium niobate layer in step S1 has a thickness of 600 nm, the silicon dioxide layer has a thickness of 4.7 μm, and the silicon substrate layer has a thickness of 0.525 mm.
[0019] Based on the above technical solutions, preferably, the low-loss thin-film lithium niobate optical waveguide has a width greater than 1 μm, the waveguide etching depth is less than 400 nm, and the waveguide sidewall tilt angle is 60-65°.
[0020] The low-loss thin-film lithium niobate optical waveguide fabrication method based on electron beam photoresist of the present invention has the following advantages over the prior art:
[0021] (1) The present invention uses electron beam photoresist as a mask, which does not require additional growth of hard mask compared with the traditional solution, and has a simpler process step.
[0022] (2) The electron beam photoresist used in this invention enables the processing accuracy of thin-film lithium niobate optical waveguides to reach the 10-nanometer level. Compared with the traditional hard mask solution, the processing accuracy is higher and the sidewall roughness is lower. Based on this, easy-to-integrate lithium niobate devices can be constructed, providing a process foundation for the development of large-scale lithium niobate integration.
[0023] (3) The present invention uses pure argon as the etching gas. Compared with the traditional method of using a mixture of argon and fluorine-based gas for etching, it does not produce lithium fluoride by-product deposition, effectively reducing the edge roughness of the waveguide and the waveguide transmission loss. Attached Figure Description
[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0025] Figure 1 This is a flowchart of the method for fabricating thin-film lithium niobate optical waveguides based on electron beam photoresist masks according to the present invention.
[0026] Figures 2a-2e According to Figure 1 The diagram illustrates the process of fabricating thin-film lithium niobate optical waveguides using the method described above. In the diagram, 1 represents the lithium niobate layer, 2 represents the silicon dioxide layer, 3 represents the silicon substrate layer, and 4 represents the photoresist mask layer.
[0027] Figure 3 Is adopted Figure 1 Scanning electron microscope (SEM) image of the waveguide cross-section obtained by the method for fabricating thin-film lithium niobate optical waveguides;
[0028] Figure 4a and 4b This is a comparison image of waveguides etched using electron beam photoresist masks versus waveguides etched using metal masks. Figure 4a For etching waveguides using electron beam photoresist masks, Figure 4b Etching waveguides using metal masks;
[0029] Figure 5a and 5b This is a comparison of the fabrication accuracy of waveguides etched with electron beam photoresist masks and waveguides etched with metal masks, both with a designed width of 1.5 μm. Figure 4a For etching waveguides using electron beam photoresist masks, Figure 4b Waveguides are etched using a metal mask. Detailed Implementation
[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0031] The developer MIBK is prepared by mixing MIBK (methyl isobutyl ketone) and IPA (isopropanol) in a volume ratio of 1:3.
[0032] Example 1
[0033] The method for fabricating low-loss thin-film lithium niobate optical waveguides based on electron beam photoresist in this embodiment includes the following steps:
[0034] S1, Obtain a thin-film lithium niobate wafer sample to be processed, such as... Figure 2a As shown, the thin-film lithium niobate comprises a 600 nm thick lithium niobate layer, a 4.7 μm thick silicon dioxide layer, and a 0.525 mm thick silicon substrate layer. Sample cleaning: The thin-film lithium niobate wafer sample was first ultrasonically treated with acetone for 8 min, then ultrasonically treated with isopropanol solution for 10 min, and finally rinsed with deionized water for 15 s.
[0035] S2, spin-coated electron beam photoresist, such as Figure 2b As shown, the thin-film lithium niobate sample was placed in a spin coater to spin coat an AR-P6200.13 photoresist layer. The spin coater was rotated at 2000 r / min for 1 min to obtain a 600 nm thick photoresist layer. After spin coating, the sample was pre-baked by placing it on a hot plate and baking it at 150 °C for 1 min.
[0036] S3, the designed mask pattern is transferred onto the photoresist layer using electron beam lithography. After lithography, the sample is post-baked at 150°C for 1 minute.
[0037] S4, such as Figure 2c As shown, the sample after electron beam lithography is developed and fixed. First, the sample is immersed in MIBK developer for 70 seconds for development. Then, the sample is removed and immersed in isopropanol fixer for 30 seconds for fixing to form a photoresist mask layer.
[0038] S5, such as Figure 2d As shown, the thin-film lithium niobate layer in the sample was etched using inductively coupled plasma etching (ICP-E). Argon was used as the etching gas, with a gas flow rate of 30 sccm, an RF power of 100 W, an ICP power of 600 W, and an etching selectivity ratio of lithium niobate to photoresist of 1.2:1. The etching rate of lithium niobate was approximately 30 nm / min. After etching for 12 min, the pattern of the photoresist mask layer was transferred onto the lithium niobate layer, forming a ridge-shaped thin-film lithium niobate optical waveguide with an etching depth of 360 nm.
[0039] S6, such as Figure 2e As shown, the residual photoresist layer on the lithium niobate layer 3 was cleaned using a photoresist remover. The sample was immersed in N-methylpyrrolidone for 2 hours to dissolve the remaining photoresist, and then the sample was removed and rinsed in deionized water for 10 seconds.
[0040] S7, such as Figure 2eAs shown, the sample was placed in an RCA solution composed of ammonia, hydrogen peroxide and deionized water in a ratio of 1:1:5 and heated in a 60°C water bath for 30 minutes to dissolve the residual organic matter on the lithium niobate layer. After that, the sample was taken out and rinsed in deionized water for 10 seconds to finally obtain a thin-film lithium niobate optical waveguide.
[0041] The low-loss thin-film lithium niobate optical waveguides prepared in this embodiment have widths of 1 μm, 1.5 μm, and 2 μm, a ridge waveguide etching depth of 360 nm, and a waveguide sidewall tilt angle of 64.2° (see...). Figure 3 ).
[0042] Example 2
[0043] The method for fabricating low-loss thin-film lithium niobate optical waveguides based on electron beam photoresist in this embodiment includes the following steps:
[0044] S1, Obtain a thin-film lithium niobate wafer sample to be processed, such as... Figure 2a As shown, the thin-film lithium niobate comprises a 600 nm thick lithium niobate layer, a 4.7 μm thick silicon dioxide layer, and a 0.525 mm thick silicon substrate layer. To clean the sample, the thin-film lithium niobate wafer sample was first ultrasonically treated with acetone for 5 min, then ultrasonically treated with isopropanol solution for 5 min, and finally rinsed with deionized water for 10 s.
[0045] S2, spin-coated electron beam photoresist, such as Figure 2b As shown, the lithium niobate thin film sample was placed in a spin coater and an AR-P6200.13 photoresist layer was spin-coated at 2000 rpm for 2 minutes to obtain a 600 nm thick photoresist layer. After spin coating, pre-baking was performed by placing the sample on a hot plate and baking it at 130°C for 2 minutes.
[0046] S3, the designed mask pattern is transferred onto the photoresist layer using electron beam lithography. After lithography, the sample is post-baked at 130℃ for 2 minutes.
[0047] S4, such as Figure 2c As shown, the sample after electron beam lithography is developed and fixed. First, the sample is immersed in MIBK developer for 70 seconds for development. Then, the sample is removed and immersed in isopropanol fixer for 30 seconds for fixing to form a photoresist mask layer.
[0048] S5, such as Figure 2dAs shown, the thin-film lithium niobate layer in the sample was etched using inductively coupled plasma etching (ICP-E). Argon was used as the etching gas, with a gas flow rate of 40 sccm, RF power of 100 W, ICP power of 600 W, and a lithium niobate to photoresist etching selectivity ratio of 1:1. The etching rate of lithium niobate was approximately 30 nm / min. After 10 min of etching, the pattern of the photoresist mask layer was transferred onto the lithium niobate layer, forming a ridge-shaped thin-film lithium niobate optical waveguide with an etching depth of 350 nm.
[0049] S6, such as Figure 2e As shown, residual photoresist on the lithium niobate layer was cleaned using a photoresist remover. The sample was immersed in N-methylpyrrolidone for 1 hour to dissolve the remaining photoresist, and then the sample was removed and rinsed in deionized water for 10 seconds.
[0050] S7, such as Figure 2e As shown, the sample was placed in an RCA solution composed of ammonia, hydrogen peroxide and deionized water in a ratio of 2:3:5 and heated in a 60°C water bath for 30 minutes to dissolve the residual organic matter on the lithium niobate layer. After that, the sample was taken out and rinsed in deionized water for 10 seconds to finally obtain a thin-film lithium niobate optical waveguide.
[0051] The low-loss thin-film lithium niobate optical waveguides prepared in this embodiment have widths of 1 μm, 1.5 μm, and 2 μm, an etching depth of 350 nm for the ridge waveguide, and a waveguide sidewall tilt angle of 60°.
[0052] Example 3
[0053] The method for fabricating low-loss thin-film lithium niobate optical waveguides based on electron beam photoresist in this embodiment includes the following steps:
[0054] S1, Obtain a thin-film lithium niobate wafer sample to be processed, such as... Figure 2a As shown, the thin-film lithium niobate comprises a 600 nm thick lithium niobate layer, a 4.7 μm thick silicon dioxide layer, and a 0.525 mm thick silicon substrate layer. To clean the sample, the thin-film lithium niobate wafer sample was first ultrasonically treated with acetone for 10 min, then ultrasonically treated with isopropanol solution for 10 min, and finally rinsed with deionized water for 15 s.
[0055] S2, spin-coated electron beam photoresist, such as Figure 2b As shown, the thin-film lithium niobate sample was placed in a spin coater and an AR-P6200.13 photoresist layer was spin-coated at 3000 r / min for 1 min to obtain a 500 nm thick photoresist layer. After spin coating, pre-baking was performed by placing the sample on a hot plate and baking it at 150℃ for 1 min.
[0056] S3, the designed mask pattern is transferred onto the photoresist layer using electron beam lithography. After lithography, the sample is post-baked at 150°C for 1 minute.
[0057] S4, such as Figure 2c As shown, the sample after electron beam lithography is developed and fixed. First, the sample is immersed in MIBK developer for 70 seconds for development. Then, the sample is removed and immersed in isopropanol fixer for 30 seconds for fixing to form a photoresist mask layer.
[0058] S5, such as Figure 2d As shown, the thin-film lithium niobate layer in the sample was etched using inductively coupled plasma etching (ICP-E). Argon was used as the etching gas, with a gas flow rate of 50 sccm, RF power of 150 W, ICP power of 800 W, and a lithium niobate to photoresist selectivity ratio of 1.3:1. The etching rate of lithium niobate was approximately 50 nm / min. After 8 min of etching, the pattern of the photoresist mask layer was transferred onto the lithium niobate layer, forming a ridge-shaped thin-film lithium niobate optical waveguide with an etching depth of 370 nm.
[0059] S6, such as Figure 2e As shown, residual photoresist on the lithium niobate layer was cleaned using a photoresist remover. The sample was immersed in acetone for 3 hours to dissolve the remaining photoresist, and then the sample was rinsed in deionized water for 30 seconds.
[0060] S7, such as Figure 2e As shown, the sample was placed in an RCA solution composed of ammonia, hydrogen peroxide and deionized water in a ratio of 1:1:5 and heated in an 80°C water bath for 60 min to dissolve the residual organic matter on the lithium niobate layer. After that, the sample was taken out and rinsed in deionized water for 30 s to finally obtain a thin-film lithium niobate optical waveguide.
[0061] The low-loss thin-film lithium niobate optical waveguides prepared in this embodiment have widths of 1 μm, 1.5 μm, and 2 μm, an etching depth of 370 nm for the ridge waveguide, and a waveguide sidewall tilt angle of 63°.
[0062] Example 4
[0063] The method for fabricating low-loss thin-film lithium niobate optical waveguides based on electron beam photoresist in this embodiment includes the following steps:
[0064] S1, Obtain a thin-film lithium niobate wafer sample to be processed, such as... Figure 2a As shown, the thin-film lithium niobate comprises a 600 nm thick lithium niobate layer, a 4.7 μm thick silicon dioxide layer, and a 0.525 mm thick silicon substrate layer. To clean the sample, the thin-film lithium niobate wafer sample was first ultrasonically treated with acetone for 8 min, then ultrasonically treated with isopropanol solution for 6 min, and finally rinsed with deionized water for 12 s.
[0065] S2, spin-coated electron beam photoresist, such as Figure 2b As shown, the lithium niobate thin film sample was placed in a spin coater and an AR-P6200.13 photoresist layer was spin-coated at 2800 r / min for 1.5 min to obtain a 500 nm thick photoresist layer. After spin coating, pre-baking was performed by placing the sample on a hot plate and baking it at 140℃ for 1.5 min.
[0066] S3 uses electron beam lithography to transfer the designed mask pattern onto the photoresist layer. After lithography, the sample is post-baked at 140℃ for 1.5 minutes.
[0067] S4, such as Figure 2c As shown, the sample after electron beam lithography is developed and fixed. First, the sample is immersed in MIBK developer for 70 seconds for development. Then, the sample is removed and immersed in isopropanol fixer for 30 seconds for fixing to form a photoresist mask layer.
[0068] S5, such as Figure 2d As shown, the thin-film lithium niobate layer in the sample was etched using inductively coupled plasma etching (ICP-E). Argon was used as the etching gas, with a gas flow rate of 40 sccm, RF power of 130 W, ICP power of 750 W, and a lithium niobate to photoresist etching selectivity ratio of 1.1:1. The etching rate of lithium niobate was approximately 45 nm / min. After 8 min of etching, the pattern of the photoresist mask layer was transferred onto the lithium niobate layer, forming a ridge-shaped thin-film lithium niobate optical waveguide with an etching depth of 360 nm.
[0069] S6, such as Figure 2e As shown, the residual photoresist layer on the lithium niobate layer 3 was cleaned using a photoresist remover. The sample was immersed in N-methylpyrrolidone or acetone for 2 hours to dissolve the remaining photoresist, and then the sample was removed and rinsed in deionized water for 20 seconds.
[0070] S7, such as Figure 2e As shown, the sample was placed in an RCA solution composed of ammonia, hydrogen peroxide and deionized water in a ratio of 2:1:5 and heated in a 75°C water bath for 50 min to dissolve the residual organic matter on the lithium niobate layer. After that, the sample was taken out and rinsed in deionized water for 25 s to finally obtain a thin-film lithium niobate optical waveguide.
[0071] The low-loss thin-film lithium niobate optical waveguides prepared in this embodiment have widths of 1 μm, 1.5 μm, and 2 μm, an etching depth of 360 nm for the ridge waveguide, and a waveguide sidewall tilt angle of 65°.
[0072] Example 5
[0073] The difference between Example 5 and Example 1 is that the etching selectivity ratio of lithium niobate to photoresist is 1:1, and the etching rate of lithium niobate is approximately 50 nm / min. The low-loss thin-film lithium niobate waveguides prepared in this example have widths of 1 μm, 1.5 μm, and 2 μm, an etching depth of 350 nm for the ridge waveguide, and a waveguide sidewall tilt angle of 64.7°.
[0074] Example 6
[0075] The difference between Example 6 and Example 1 is that the ratio of ammonia water:hydrogen peroxide:deionized water in the RCA solution is 2:1:5. The low-loss thin-film lithium niobate optical waveguides prepared in this example have widths of 1 μm, 1.5 μm, and 2 μm, a ridge waveguide etching depth of 360 nm, and a waveguide sidewall tilt angle of 63.8°.
[0076] Comparative Example 1
[0077] Comparative Example 1 uses the traditional thin-film lithium niobate waveguide fabrication method, employing a Cr mask to etch the thin-film lithium niobate, and using a 1:1 mixture of argon and fluorine-based gas for etching.
[0078] Comparative Example 2
[0079] Comparative Example 2 uses the traditional thin-film lithium niobate waveguide fabrication method, employing a Cr mask to etch the thin-film lithium niobate, and using a 1:2 mixture of argon and fluorine-based gas for etching.
[0080] The waveguides prepared in Comparative Examples 1-2 have large edge roughness, obvious deposition, and their actual size is smaller than the design size. Figure 4a and Figure 5a The waveguide prepared in Example 1 Figure 4b and Figure 5b As shown in Figure 4, compared to the waveguide etched by electron beam photoresist, the waveguide etched by metal mask has a larger edge roughness and more obvious deposition, which increases the waveguide transmission loss. Figure 5 shows that the actual size of the waveguide etched by electron beam photoresist is within 20 nm of the design size, while the actual size of the waveguide etched by metal mask exceeds 270 nm.
[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for fabricating a low-loss thin-film lithium niobate optical waveguide based on electron beam photoresist, characterized in that: Includes the following steps: S1, a pre-prepared thin-film lithium niobate wafer is provided as a substrate, wherein the thin-film lithium niobate wafer comprises, from bottom to top, a silicon substrate layer, a silicon dioxide layer and a thin-film lithium niobate layer; S2, spin-coating electron beam photoresist onto the surface of the thin film lithium niobate layer, and pre-baking the photoresist; S3, the mask pattern is transferred onto the photoresist using electron beam exposure after drying, and the sample is then post-baked; The methods for pre-baking and post-baking in steps S2 and S3 are as follows: place the sample on a heating plate and bake at 130-150℃ for 1-2 minutes; S4, the dried photoresist is sequentially developed and fixed to form a photoresist mask layer, and then the thin film lithium niobate layer is etched by inductively coupled plasma etching process to transfer the pattern on the photoresist to the thin film lithium niobate layer. The etching gas is argon. S5, remove the residual photoresist on the thin film lithium niobate layer to obtain a low-loss thin film lithium niobate optical waveguide; In step S2, the electron beam photoresist used is AR-P 6200.13, the spin coating speed is 2000-3000 r / min, and the spin coating time is 1-2 min. During the etching process in step S4, the argon gas flow rate is 30-50 sccm, the radio frequency power is 100-150W, the ICP power is 600-800W, the etching selectivity ratio of lithium niobate to photoresist is (1-1.3):1, and the etching rate of lithium niobate is 30-50 nm / min. After etching for 8-12 min, the pattern of the photoresist mask layer is transferred to the lithium niobate layer to form a ridge-shaped thin film lithium niobate optical waveguide with an etching depth of 350-370 nm.
2. The method for fabricating a low-loss thin-film lithium niobate optical waveguide based on electron beam photoresist as described in claim 1, characterized in that: In step S2, the thin-film lithium niobate wafer needs to be cleaned before spin-coating the electron beam photoresist. The cleaning method is as follows: first, place the thin-film lithium niobate sample in acetone and sonicate for 5-10 minutes, then place it in isopropanol solution and sonicate for 5-10 minutes, and then rinse it in deionized water for 10-15 seconds.
3. The method for fabricating a low-loss thin-film lithium niobate optical waveguide based on electron beam photoresist as described in claim 1, characterized in that: The method for removing residual photoresist in step S5 is as follows: immerse the sample in a photoresist remover solution for 1-3 hours to dissolve the remaining photoresist, and then take out the sample and rinse it under deionized water for 10-30 seconds; the photoresist remover solution is N-methylpyrrolidone or acetone.
4. The method for fabricating a low-loss thin-film lithium niobate optical waveguide based on electron beam photoresist as described in claim 3, characterized in that: After removing the residual photoresist in step S5, it is also necessary to remove the residual organic byproducts. The method is as follows: place the sample in the cleaning solution and heat it in a water bath at 60℃-80℃ for 30-60 minutes to dissolve the residual organic matter on the lithium niobate layer. Then take out the sample and rinse it in deionized water for 10-30 seconds to finally obtain the thin film lithium niobate optical waveguide. The cleaning solution is prepared by ammonia water: hydrogen peroxide: deionized water in a volume ratio of (1-2): (1-3):
5.
5. The method for fabricating a low-loss thin-film lithium niobate optical waveguide based on electron beam photoresist as described in claim 1, characterized in that: The lithium niobate layer in step S1 has a thickness of 600 nm, the silicon dioxide layer has a thickness of 4.7 μm, and the silicon substrate layer has a thickness of 0.525 mm.
6. The method for fabricating a low-loss thin-film lithium niobate optical waveguide based on electron beam photoresist as described in claim 1, characterized in that: The low-loss thin-film lithium niobate optical waveguide has a width greater than 1 μm, an etching depth of less than 400 nm, and a waveguide sidewall tilt angle of 60-65°.