Etching method of thin-film lithium niobate optical waveguide chip

Abstract

The invention discloses an etching method of a thin-film lithium niobate optical waveguide chip, which is characterized in that thin-film lithium niobate is etched in a stepped high-temperature hardening mode in a vacuum environment, and deposition and stripping steps required by a dielectric mask and a metal mask are avoided by using a photoresist mask. The process can be completed only by performing vacuum high-temperature treatment through a high-temperature annealing furnace after developing, and the time for forming a hard film can be shortened by adjusting the power of the annealing furnace; by utilizing stepped high-temperature hardening in a vacuum environment and combining the high-temperature tolerance of the photoresist, oxidation reaction is avoided, and the hardness and the selection ratio of the photoresist mask are remarkably improved; the ICP etching instrument is adopted for physical etching, traditional chemical etching is replaced, deposition of by-products is avoided, and the 65-degree side wall inclination angle is achieved; furthermore, in the dry etching process, etching is carried out in a circulating process, so that the anisotropy of the thin-film lithium niobate optical waveguide chip is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of thin-film lithium niobate optical waveguide chips, and in particular relates to an etching method for thin-film lithium niobate optical waveguide chips. Background Art

[0002] In the preparation process of thin-film lithium niobate, the etching process is an important step. Achieving a high etching selectivity and smooth sidewalls has always been a process difficulty. The current mainstream etching processes include chemical mechanical polishing (CMP), wet etching, and dry etching. CMP has difficulty in achieving a small bending radius, which seriously limits the device size, and wet etching is easily affected by the crystal defects of lithium niobate due to the anisotropy of the crystal. Relatively speaking, mutually coupled plasma etching (CMP) uses high-density plasma to react chemically with the etching material and the physical effect generated by the reaction particles to perform etching, which has the characteristics of fast etching rate, large selectivity, and high degree of anisotropic etching. Therefore, ICP is widely used in the processing of thin-film lithium niobate.

[0003] Currently, masks for dry etching of lithium niobate (LNbO) typically use dielectrics (e.g., SiO2, SiN) or metals (e.g., Cr, Al). These require additional deposition and stripping steps, making the process complex and susceptible to material damage. Photoresist masks simplify the process, but they offer poor etch resistance. Existing high-temperature hardening techniques utilize a gradient temperature ramp, but these processes are not optimized for the characteristics of LNbO and lack a vacuum environment, leading to oxidation and degradation of the photoresist and insufficient selectivity.

[0004] Directly using photoresist as a mask not only simplifies the process but also maintains the flatness of the sidewalls and the optical properties of the lithium niobate material. However, the photoresist mask has poor etch resistance, resulting in a low selectivity between the photoresist and lithium niobate. During deep etching of the lithium niobate film, the photoresist is nearly depleted, resulting in rounded corners on the etched sidewalls, which cannot meet etching requirements. Improving the selectivity of the photoresist mask is an urgent challenge that needs to be overcome. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a method for etching a thin-film lithium niobate optical waveguide chip. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0006] The present invention provides a method for etching a thin-film lithium niobate optical waveguide chip, comprising:

[0007] preparing a photoresist mask on the surface of thin film lithium niobate;

[0008] Performing a step-by-step high-temperature hardening treatment on the photoresist mask on the surface of the lithium niobate thin film in a vacuum environment;

[0009] The thin film lithium niobate is dry-etched using an ICP etcher to obtain an etched chip;

[0010] wet-etching the etched chip in a chemical solution to remove etching byproducts to obtain a first processed chip;

[0011] Processing the first processing chip with a buffered oxide to remove photoresist residues from etching to obtain a second processing chip;

[0012] placing the second processing chip in deionized water and removing the remaining solution to obtain a third processing chip;

[0013] The third processed chip was blown dry with nitrogen to obtain an etched thin film lithium niobate optical waveguide chip.

[0014] In one embodiment of the present invention, a photoresist mask is prepared on the surface of a thin film of lithium niobate, comprising:

[0015] The cleaned lithium niobate thin film is placed in a HMDS drying oven for pretreatment;

[0016] The pre-treated thin-film lithium niobate is subjected to coating, pre-baking, electron beam exposure and development treatments to obtain a photoresist mask on the surface of the thin-film lithium niobate.

[0017] In one embodiment of the present invention, during the process of coating, the rotation speed is set to 750-900 rpm, and the photoresist used is HSQ with a thickness of 0.5-1.5 μm.

[0018] In one embodiment of the present invention, a stepwise high-temperature hardening process is performed on a photoresist mask on a surface of a lithium niobate thin film in a vacuum environment, comprising:

[0019] The lithium niobate thin film with a photoresist mask on its surface is placed in a high-temperature annealing furnace and evacuated, and the pressure in the furnace is maintained below -1 bar;

[0020] The process is carried out according to the preset temperature control program to obtain a stepped high-temperature hard film.

[0021] In one embodiment of the present invention, the preset temperature control program includes:

[0022] Heat up to 450℃ in 40 minutes and keep it warm for 20 minutes; heat up to 500℃ in 60 minutes and keep it warm for 60 minutes; cool down to 450℃ in 60 minutes and keep it warm for 20 minutes; then cool down naturally to room temperature.

[0023] In one embodiment of the present invention, an ICP etcher is used to dry-etch a thin film of lithium niobate to obtain an etched chip, comprising:

[0024] The etching is performed in a cyclic process with a number of cycles of 4-6 times; wherein, the process of one cycle includes:

[0025] The surface of the thin film lithium niobate is cleaned using 20-50 sccm of O2 at an ICP source power of 0-60 W and an RF bias power of 50-100 W to obtain a cleaned device;

[0026] The cleaned device was etched using 10-50 sccm of Ar at an ICP source power of 200-300 W and an RF bias power of 120-180 W.

[0027] In one embodiment of the present invention, the chemical solution comprises:

[0028] NH4OH, H2O2 and water are mixed in a first preset ratio; wherein,

[0029] The first preset ratio is 5:1:1.

[0030] In one embodiment of the present invention, during the process of treating the first processing chip with the buffered oxide, the solution used is HF and water in a volume ratio of 1:7, and the treatment time is 5-8 minutes.

[0031] Beneficial effects of the present invention:

[0032] The solution provided by the present invention utilizes a step-by-step high-temperature hardening method in a vacuum environment to etch thin-film lithium niobate. A photoresist mask is used to avoid the deposition and stripping steps required for dielectric and metal masks. After development, the etching can be completed by simply performing vacuum and high-temperature annealing in a high-temperature annealing furnace. Adjusting the annealing furnace power can reduce the time required for hardening. The step-by-step high-temperature hardening method in a vacuum environment, combined with the high-temperature tolerance of the photoresist, avoids oxidation reactions, significantly improving the hardness and selectivity of the photoresist mask. Physical etching using an ICP etcher replaces traditional chemical etching, avoiding byproduct deposition and achieving a 65° sidewall tilt angle. Furthermore, a cyclic etching process is employed during dry etching, thereby improving the anisotropy of the thin-film lithium niobate optical waveguide chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the steps of an etching method for a thin-film lithium niobate optical waveguide chip provided by an embodiment of the present invention;

[0034] Figure 2 A process flow chart of an etching method for a thin-film lithium niobate optical waveguide chip provided by an embodiment of the present invention;

[0035] Figure 3 A temperature variation curve of high-temperature film hardening at 500°C in an etching method for a thin-film lithium niobate optical waveguide chip provided by an embodiment of the present invention;

[0036] Figure 4a-4b SEM comparison images of the cross-section of a thin-film lithium niobate optical waveguide chip before and after high-temperature hardening at 400° C. in an etching method of the thin-film lithium niobate optical waveguide chip provided by an embodiment of the present invention;

[0037] Figure 5a-5b SEM comparison of thin-film lithium niobate optical waveguide chips after ICP etching with and without high-temperature hardened films in an etching method for thin-film lithium niobate optical waveguide chips provided by an embodiment of the present invention;

[0038] Figure 6a-6b Surface SEM comparison images of a thin-film lithium niobate optical waveguide chip before and after being etched by a chemical solution in an etching method of the thin-film lithium niobate optical waveguide chip provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0039] Figure 2 The process flow chart of the etching method of a thin film lithium niobate optical waveguide chip provided by the embodiment of the present invention is as follows. Figure 2 The present invention is further described in detail with reference to the accompanying drawings and specific examples, but the embodiments of the present invention are not limited thereto.

[0040] The embodiment of the present invention provides a method for etching a thin film lithium niobate optical waveguide chip, such as Figure 1 As shown, this may include:

[0041] S1, prepare a photoresist mask on the surface of the thin film lithium niobate, such as Figure 2 As shown, this may include:

[0042] S11, pre-treating the cleaned lithium niobate thin film in a HMDS (Hexamethyl disilylamine) drying oven;

[0043] S12, performing coating, pre-baking, electron beam exposure and development treatment on the pre-treated lithium niobate thin film to obtain a photoresist mask on the surface of the lithium niobate thin film.

[0044] Specifically, in S11, the pretreatment changes the surface of lithium niobate from hydrophilic to hydrophobic, thereby improving the adhesion of the photoresist on the surface of lithium niobate and avoiding problems such as drifting stripes and floating glue.

[0045] For S12, the process flow chart is as follows Figure 2As shown, when using a spin coater to spin-coat photoresist on a surface, a certain thickness is required to maintain the etching depth. During the spin coat process, the spin coat speed can be set to 750-900 rpm. High-pressure silica (HSQ) photoresist with a thickness of 0.5-1.5 μm is used. The device is then pre-baked on a hot plate to remove most of the solvent in the photoresist, improving adhesion and thickness uniformity. This increases exposure accuracy, prevents solubility variations during subsequent development, and improves mask linewidth control. The temperature is set to approximately 120°C. High-precision exposure is achieved using an electron beam. Electron beams are essentially charged particles. Due to the wave-particle duality, increasing the electron beam's acceleration voltage can reduce the wavelength and improve exposure accuracy. After development, the designed pattern is transferred to the photoresist, forming a photoresist mask.

[0046] S2, performing a step-by-step high-temperature hardening treatment on the photoresist mask on the surface of the lithium niobate thin film in a vacuum environment, which may include:

[0047] The lithium niobate thin film with a photoresist mask on its surface is placed in a high-temperature annealing furnace and evacuated, and the pressure in the furnace is maintained below -1 bar;

[0048] The process is carried out according to the preset temperature control program to obtain a stepped high-temperature hard film.

[0049] It is understandable that the decomposition temperature of many photoresists is generally between 100 and 130°C. However, the photoresist used in the embodiments of the present invention is hydrogen silsesquioxane (HSQ), which has a higher decomposition temperature (400°C) and glass transition temperature (380°C). HSQ gradually solidifies as the temperature rises and can withstand higher temperatures. By reducing the solvent content in the photoresist, especially near the bottom of the lithium niobate mask, the hardening effect is better. Increasing the hardness of the mask and thus improving the etching selectivity.

[0050] The temperature change curve of high temperature hard film at 500℃, such as Figure 3 As shown, it can be seen that the preset temperature control program may include:

[0051] Heat to 450°C in 40 minutes and keep warm for 20 minutes, heat to 500°C in 60 minutes and keep warm for 60 minutes, cool to 450°C in 60 minutes and keep warm for 20 minutes, and then cool naturally to room temperature.

[0052] Specifically, a lithium niobate sample was placed in an annealing furnace for 60 minutes to reach the required hardening temperature, and then hardened for another 60 minutes. The glass transition temperature (GTT) is the temperature at which a material transitions from a glassy state to a highly elastic state, significantly affecting the morphology of the mask. On the one hand, HSQ softens, and if left for too long, it can lead to blurred patterns and rounded corners at the top of the photoresist, further affecting the morphology of the etched sidewalls. However, too short a time prevents the molecular chains from fully extending and adjusting, resulting in excessive stress in the mask layer. While the hardening temperature is between 400 and 500°C, and although the GTT has been reached, SEM characterization shows no noticeable changes in the photoresist, and the resulting waveguides show no changes in size or morphology. This is primarily due to the fact that the embodiment of the present invention is maintained at 400°C (slightly above the GTT) for 60 minutes before gradually raising the temperature to the hardening temperature. This reduces thermal stress, maintaining a stable morphology, while also allowing the material to fully solidify, preventing excessive temperatures from causing noticeable HSQ glass transition. The temperature is then raised to the set hardening temperature. Similarly, to reduce problems such as cracking on the mask surface caused by drastic temperature fluctuations during the cooling process, HSQ can withstand very high temperatures, which greatly expands its range of use as a photoresist mask. However, HSQ's performance varies greatly at different temperatures, so a step-by-step temperature increase is necessary.

[0053] It's important to note that hardening the film must be performed in a vacuum environment and allowed to cool naturally to room temperature. During the baking process, the residual solvent content further decreases, reducing the elasticity of the photoresist structure. Simultaneously, the photoresist reacts with oxygen, causing the photoresist to become brittle around 120-130°C. The different thermal expansion coefficients of the photoresist and substrate materials can lead to cracks. For example, invisible stress cracks may form on thick films, potentially causing problems during subsequent etching. Therefore, high-temperature vacuum annealing is necessary, primarily to prevent the photoresist from reacting with oxygen. At temperatures exceeding 400°C, HSQ readily reacts with oxygen, converting Si-H to Si-O-Si. However, the water produced by this reaction can evaporate at high temperatures or generate hydrogen, causing the photoresist mask to collapse, surface roughening, and increasing stress between the photoresist and the lithium niobate. This can lead to surface degradation and roughening during subsequent etching processes, which is unacceptable for optical devices. Therefore, after placing the lithium niobate film in the annealing furnace, the vacuum pump is first activated until the pressure inside the furnace drops to -1 bar. The annealing furnace valve is then closed to maintain a sealed state to prevent reaction between the photoresist and oxygen. At the same time, the cooling rate is controlled to minimize crack formation. Natural cooling is used here to prevent brittle cracking caused by excessive temperature drops.

[0054] The embodiment of the present invention adopts a step-by-step high-temperature hardening process in a vacuum environment, combined with the high-temperature tolerance of HSQ photoresist (decomposition temperature 400° C.), to avoid oxidation reactions and significantly improve the mask hardness and selectivity.

[0055] SEM comparison of the cross section of the thin film lithium niobate optical waveguide chip before and after high temperature hardening at 400℃, as shown in the figure. Figure 4a-4b As shown, Figure 4a Before the hard membrane, Figure 4b After hardening, it can be seen that after vacuum hardening at 400℃, the thickness of the photoresist mask only decreases by 2%. The high-temperature hardening of the waveguide causes a certain decrease in the thickness of the mask, but it is not obvious.

[0056] S3, dry etching the lithium niobate thin film using an ICP etcher to obtain an etched chip, may include:

[0057] The etching is performed in a cyclic process with a number of cycles of 4-6 times; wherein, the process of one cycle includes:

[0058] The surface of the thin film lithium niobate is cleaned using 20-50 sccm of O2 at an ICP source power of 0-60 W and an RF bias power of 50-100 W to obtain a cleaned device;

[0059] The cleaned device was etched using 10-50 sccm of Ar at an ICP source power of 200-300 W and an RF bias power of 120-180 W.

[0060] Specifically, during the cycle, the lithium niobate sample is sent into a vacuum chamber, and the sample surface is first cleaned with oxygen, and then enters the cycle. At the beginning of the cycle, oxygen ions are used to clean the sample in order to reduce the heavy deposition effect. In ion beam milling, there are non-volatile by-products that precipitate on the etched surface, which not only reduces the etching rate and hinders the further progress of etching, but also causes the etched sidewall to tilt, which is not conducive to morphology control and may cause secondary effects, resulting in grooving at the bottom of the groove. At the same time, it will increase the roughness of the etched surface after etching, reduce the inherent optical properties of the lithium niobate material, and is not conducive to the subsequent possible metal electrode evaporation.

[0061] Therefore, the chip surface is cleaned with 20-50 sccm of O2, an ICP source power of 0-60 W, and an RF bias power of 50-100 W. The RF bias power must be kept moderate; too low a level will not clean effectively, while too high a level will affect the morphology of the photoresist mask. The oxygen cleaning cycle lasts 5-30 seconds.

[0062] Ar milling is a purely physical etching. When the gas volume gradually increases, the etching rate can be increased. However, when the gas volume gradually reaches saturation, the excess gas does not have time to plasmatize and is diluted by the subsequent gas, resulting in a decrease in the etching rate. Similarly, ICP is the power of the inductively coupled plasma source (also called the upper electrode power). Increasing the ICP power can increase the plasma activation rate and thus increase the number of plasmas. RF power mainly accelerates the plasma, but there is a speed saturation phenomenon. Increasing the RF bias power can control the inclination angle of the etched sidewall.

[0063] In order to improve the verticality of the side wall, the chamber vacuum is controlled, the gas pressure is 2 to 3 mTorr, and the free path is increased, so that the plasma has a greater probability of entering the deep groove, thereby improving the verticality of the etched side wall and the aspect ratio of the groove.

[0064] Ar physical etching replaces traditional Cl2 / H2 chemical etching to avoid byproduct deposition and achieve a 65° sidewall tilt. Anisotropy can be improved by optimizing cyclic etching parameters (ICP power 200-300 W, RF bias 120-180 W).

[0065] The Ar etching time is 2-3 minutes. A time that is too short will increase the number of cycles, increasing the manufacturing cycle and cost. A time that is too long will aggravate the re-deposition effect, increase surface impurities and unevenness, and affect surface smoothness. To ensure economical etching and etching effect, the etching time is kept at 2-3 minutes. The number of etching cycles is 4-6, and the specific number of cycles can be determined by the etching rate and the required etching depth.

[0066] SEM comparison of thin-film lithium niobate optical waveguide chips with and without high-temperature hardening films after ICP etching, as shown in the figure below. Figure 5a and Figure 5b As shown, Figure 5a It is etching without high temperature hardening film. Figure 5b This is the etching after high-temperature hardening. It can be seen that at a similar etching depth, the mask after high-temperature hardening is obviously thicker. At a similar etching depth, the mask after high-temperature hardening is nearly 100nm thicker than the untreated mask. The etching selectivity is increased from 0.55 to 1, which significantly improves the etching selectivity and stabilizes the sidewall inclination angle at 65°±2°.

[0067] It is understandable that the etched chip needs to be post-processed to remove heavy deposits and residual photoresist and other organic matter during etching. The specific post-processing steps include S4-S7.

[0068] S4, wet etching the etched chip in a chemical solution to remove etching byproducts to obtain a first processed chip.

[0069] Chemical solutions may include:

[0070] NH4OH, H2O2 and water are mixed in a first preset ratio; wherein,

[0071] The first preset ratio is 5:1:1.

[0072] The removal principle is that hydrogen peroxide oxidizes the surface of amorphous lithium niobate and heavy precipitates caused by Ar plasma bombardment, making them susceptible to corrosion by ammonium hydroxide. At the same time, the mechanical energy of the ammonia and oxygen bubbles generated by decomposition and the vibration causes the precipitates to fall and promotes micro-corrosion.

[0073] The surface SEM comparison of the thin film lithium niobate optical waveguide chip before and after being corroded by chemical solution, as shown in the figure. Figure 6a and Figure 6b As shown, Figure 6a Before processing, Figure 6b After treatment, it can be seen that the sediment on the chip surface has been significantly removed and the surface has become smoother.

[0074] S5, processing the first processing chip using buffered oxide (BOE) to remove the photoresist remaining after etching, thereby obtaining a second processing chip.

[0075] The buffered oxide treatment of the first processing chip uses a solution of HF and water in a volume ratio of 1:7 for 5-8 minutes. The removal mechanism is that HF converts the HSQ (which, after solidification, is primarily a Si-O-Si cage structure) into soluble SiF4.

[0076] During the S3 etching process, the chip surface undergoes oxygen plasma cleaning, which removes some heavy deposits, but the removal capacity is limited. The oxygen ion bombardment oxidizes some lithium niobate into niobium oxide and lithium oxide. It also modifies some photoresist into silicon dioxide. Therefore, wet etching with chemical solutions and BOE (buffered oxide ether) etching solutions are required to remove heavy deposits and photoresist residue, respectively.

[0077] S6, placing the second processing chip in deionized water, removing the residual solution, and obtaining a third processing chip.

[0078] The NH4OH, H2O2, and HF solutions used in the etching process may leave a small amount of chemical residue on the surface of the optical waveguide. Placing the chip in deionized water can effectively remove these residues, ensuring the cleanliness and purity of the optical waveguide surface. Deionized water has high purity and low ion content, and will not cause secondary contamination or corrosion to the optical waveguide surface. This ensures that the optical waveguide surface maintains good chemical stability and optical properties after etching. Deionized water can effectively reduce the impact of the medium on the performance of the optical waveguide, improving the stability and reliability of the device. This is especially important for optical devices that require long-term stable operation. Incorporating a deionized water cleaning step into the etching method can improve the entire process flow and ensure the quality and consistency of each step. This helps to improve manufacturing efficiency and reduce defect rates.

[0079] S7, drying the third processed chip with nitrogen to obtain an etched thin-film lithium niobate optical waveguide chip.

[0080] Specifically, nitrogen drying can effectively remove residual moisture and prevent water spots from being left on the surface of the device. This is particularly important for the optical performance of the optical waveguide, as water spots may cause scattering or loss of light transmission, and can prevent the device from undergoing oxidation reactions in the air, maintaining the cleanliness and stability of the surface. Using nitrogen to dry can also effectively avoid leaving ionic contaminants on the surface, which may affect the electrical properties and long-term stability of the optical waveguide. It is easy to understand that nitrogen drying is a fast and effective step that can quickly dry the surface of the device, shorten the manufacturing cycle, and improve production efficiency. In addition, nitrogen is a harmless and environmentally friendly gas. Using nitrogen to dry avoids the use of organic solvents or other drying methods that may be harmful to the environment, meeting the requirements of green manufacturing. The surface of the optical waveguide chip after drying is clean and free of water spots, and provides a clean and stable foundation for subsequent subsequent processing steps, such as packaging and testing of optical waveguide devices.

[0081] It is understandable that the embodiment of the present invention provides a method for etching a thin-film lithium niobate optical waveguide chip, which uses a step-by-step high-temperature hardening method in a vacuum environment to etch the thin-film lithium niobate, which has the advantages of simple process and high selectivity. Specifically:

[0082] In terms of process, the photoresist mask avoids the deposition and stripping steps required for dielectric masks and metal masks, and can be completed only after development through a high-temperature annealing furnace with a vacuum pump under vacuum and high temperature. By adjusting the power of the annealing furnace, the time required for hardening can be reduced, avoiding complex processes such as vacuum magnetron sputtering of chromium metal, chlorine etching of the metal mask layer, and preparation of chromium cleaning solution. The high-temperature hardening process has been optimized to address the difficulties in lithium niobate etching. The hardening temperature used is much higher than 200°C, which is necessary to maintain the chemical properties of the photoresist in a vacuum environment. After reaching the glass transition temperature, it is also necessary to optimize the time and temperature parameters of the step-by-step temperature change. The embodiment of the present invention adopts such a combination of technologies based on the characteristics of lithium niobate materials and their common photoresists in order to achieve high-quality lithium niobate etching based on a simplified process flow.

[0083] In terms of selectivity, by adjusting the temperature of the annealing furnace and the rate of temperature increase and decrease, the hardness of the photoresist can be effectively controlled, thereby adjusting the selectivity. This also reduces the required photoresist thickness, minimizes secondary effects, and improves the aspect ratio of the etching. To achieve high-selectivity lithium niobate etching, there are two main approaches. The first is to improve the etching resistance of the mask, primarily by using dielectric masks such as silicon dioxide or metal masks such as chromium. The present invention utilizes the HSQ high-temperature hardening process, which avoids the need for additional process steps such as mask deposition, pattern transfer, and mask layer removal, thereby reducing process complexity. The second approach is to improve the lithium niobate etching efficiency while maintaining etching anisotropy. The use of fluorine-based gases produces lithium fluoride as a byproduct, which is difficult to volatilize. Precipitation of this byproduct at the bottom of the newly etched lithium niobate groove hinders further etching, making it difficult to effectively improve even with a higher bias voltage. Furthermore, lithium fluoride precipitation on the sidewalls of the etched groove can cause the sidewall inclination to be less than vertical. While using chlorine-based gases can avoid precipitated byproducts, their etching efficiency is too high for common masks, making it difficult to achieve high etching selectivity. The Ar plasma etching used in this invention is a purely physical etching method with high anisotropy. The etching direction is perpendicular to the film surface, and its directionality and rate can be further enhanced by adjusting the RF bias voltage, thereby achieving high etching selectivity.

[0084] Therefore, embodiments of the present invention utilize a step-by-step high-temperature hardening method in a vacuum environment to etch thin-film lithium niobate. Using a photoresist mask, the deposition and stripping steps required for dielectric and metal masks are avoided. After development, the etching can be completed by simply performing vacuum and high-temperature annealing in a high-temperature annealing furnace. By adjusting the power of the annealing furnace, the time required for hardening can be reduced. The step-by-step high-temperature hardening method in a vacuum environment, combined with the high-temperature tolerance of the photoresist, avoids oxidation reactions, significantly improving the hardness and selectivity of the photoresist mask. Physical etching using an ICP etcher replaces traditional chemical etching, avoiding the deposition of byproducts and achieving a 65° sidewall tilt angle. Furthermore, during dry etching, a cyclic process is employed to enhance the anisotropy of the thin-film lithium niobate optical waveguide chip. The embodiment of the present invention uses a photoresist as a mask to etch a lithium niobate thin film, which has the advantages of simple process and high selectivity. The etching depth can reach 370nm, the etching morphology is good, the inclination angle of the etched sidewall and bottom can reach 65°, and the etching has no obvious degradation on the performance of the lithium niobate material. Compared with the traditional method, the selectivity obtained in the embodiment of the present invention is improved by about 50%, the sidewall inclination angle accuracy is also improved, and the process flow is reduced by 3 steps.

[0085] It should be noted that, in the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. A method for etching a thin-film lithium niobate optical waveguide chip, characterized in that: include: preparing a photoresist mask on the surface of thin film lithium niobate; The photoresist mask on the surface of the thin film lithium niobate is subjected to a step-by-step high-temperature hardening treatment in a vacuum environment; The thin film lithium niobate is dry-etched using an ICP etcher to obtain an etched chip; wet-etching the etched chip in a chemical solution to remove etching byproducts to obtain a first processed chip; Processing the first processing chip with a buffered oxide to remove residual photoresist after etching to obtain a second processing chip; placing the second processing chip in deionized water and removing the remaining solution to obtain a third processing chip; The third processed chip was blown dry with nitrogen to obtain an etched thin film lithium niobate optical waveguide chip.

2. The etching method of a thin film lithium niobate optical waveguide chip according to claim 1, characterized in that: The method of preparing a photoresist mask on the surface of the lithium niobate thin film comprises: The cleaned lithium niobate thin film is placed in a HMDS drying oven for pretreatment; The pre-treated thin-film lithium niobate is subjected to coating, pre-baking, electron beam exposure and development treatments to obtain a photoresist mask on the surface of the thin-film lithium niobate.

3. The etching method of a thin film lithium niobate optical waveguide chip according to claim 2, characterized in that: During the process of coating, the rotation speed is set to 750-900 rpm, and the photoresist used is HSQ with a thickness of 0.5-1.5 μm.

4. The etching method of a thin film lithium niobate optical waveguide chip according to claim 1, characterized in that: The stepwise high-temperature hardening treatment of the photoresist mask on the surface of the lithium niobate thin film in a vacuum environment comprises: The lithium niobate thin film with a photoresist mask on its surface is placed in a high-temperature annealing furnace and evacuated, and the pressure in the furnace is maintained below -1 bar; The process is carried out according to the preset temperature control program to obtain a stepped high-temperature hard film.

5. The etching method of a thin film lithium niobate optical waveguide chip according to claim 4, characterized in that: The preset temperature control program includes: Heat to 450°C in 40 minutes and keep warm for 20 minutes, heat to 500°C in 60 minutes and keep warm for 60 minutes, cool to 450°C in 60 minutes and keep warm for 20 minutes, and then cool naturally to room temperature.

6. The etching method of a thin film lithium niobate optical waveguide chip according to claim 1, characterized in that: The method of dry-etching the thin film lithium niobate using an ICP etcher to obtain an etched chip comprises: The etching is performed in a cyclic process with a number of cycles of 4-6 times; wherein, the process of one cycle includes: The surface of the thin film lithium niobate is cleaned using 20-50 sccm of O2 at an ICP source power of 0-60 W and an RF bias power of 50-100 W to obtain a cleaned device; The cleaned device was etched using 10-50 sccm of Ar at an ICP source power of 200-300 W and an RF bias power of 120-180 W.

7. The etching method of a thin film lithium niobate optical waveguide chip according to claim 1, characterized in that: The chemical solution comprises: NH4OH, H2O2 and water are mixed in a first preset ratio; wherein, The first preset ratio is 5:1:

1.

8. The etching method for a thin-film lithium niobate optical waveguide chip according to claim 1, characterized in that: In the process of treating the first processing chip with the buffered oxide, the solution used is HF and water in a volume ratio of 1:7, and the treatment time is 5-8 minutes.

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