Lithium niobate micro-nano structures, dry etching method for forming the same and applications thereof

Abstract

The application discloses a lithium niobate micro-nano structure, a dry etching method for forming the same and application of the lithium niobate micro-nano structure. The dry etching method comprises the following steps: providing a lithium niobate base; forming a patterned mask on the surface of the lithium niobate base; and performing etching treatment on the lithium niobate base by using a magnetic neutral loop discharge etching method to form a micro-nano structure; wherein the temperature of the lithium niobate base is maintained to be not lower than 400 DEG C during the etching treatment, and the etching treatment is performed in an intermittent cycle mode. The application uses the magnetic neutral loop discharge etching method to intermittently etch the lithium niobate at high temperature, accelerates the etching rate in the vertical direction, and the generated product in the reaction process is rapidly volatilized under the influence of high temperature, so that the etching perpendicularity of the micro-nano structure is greatly improved; the photoresist can be directly used as a mask to prepare the lithium niobate micro-nano structure with a high aspect ratio, and the steps of preparing a metal or dielectric hard mask are avoided, so that the preparation process is greatly simplified, and the processing cost is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of micro-nano manufacturing technology, and in particular to a lithium niobate micro-nano structure, a dry etching method for forming the structure, and its application. Background Technology

[0002] Integrated photonics has broad application prospects in communication, sensing, and computing. Because the manufacturing processes for silicon chips in integrated circuits are very mature, and silicon happens to be transparent and has a high refractive index in the optical communication band, CMOS processes can be used to mass-produce silicon-based integrated optical circuits. "Silicon photonics" has developed in this context. In addition, technologies based on materials such as indium phosphide (InP), silicon nitride (SiNx), gallium arsenide (GaAs), aluminum nitride (AlN), and silicon carbide (SiC) are also under development. However, these materials cannot simultaneously support ultra-low propagation loss, fast low-loss optical modulation, and efficient all-optical nonlinearity. Lithium niobate (LiNbO3, LN) possesses a transparent window from the visible to mid-infrared band (0.35μm~5μm), a relatively high refractive index, excellent electro-optic and second-order nonlinear optical properties, and outstanding acousto-optic and piezoelectric properties, earning it the title of "optical silicon," and it can be widely used in integrated photonics.

[0003] Lithium niobate thin films can be used to fabricate ultra-high performance compact modulators, broadband frequency combs, and high-efficiency optical frequency converters and single-photon sources. Doped lithium niobate materials also have a wide range of applications. Mg:LN can significantly improve the laser damage threshold, promoting the application of lithium niobate crystals in nonlinear optics; Nd:Mg:LN crystals can achieve self-frequency doubling; Fe:LN crystals are used for optical bulk holographic storage. Therefore, researching the fabrication technology of high-quality lithium niobate thin films and developing high-precision lithium niobate nanostructure processing techniques is crucial!

[0004] However, existing lithium niobate etching technologies mostly employ reactive ion etching (RIE), inductively coupled plasma etching (ICP), ion beam etching (IBE), wet etching (WE), and combinations thereof. All of these techniques require a dielectric-metal hybrid hard mask on the lithium niobate surface, increasing the fabrication steps and process complexity, significantly raising costs. Furthermore, due to technological limitations, it is currently difficult to fabricate nanoscale lithium niobate micro / nanostructures with high aspect ratios and high verticality. While focused ion beam etching (FIB) is a high-precision etching technique that does not require a hard mask, and some studies have reported its potential for fabricating high-quality lithium niobate micro / nanostructures, its etching speed is extremely slow, and its cost is prohibitively high, hindering the large-scale production and commercialization of lithium niobate micro / nano devices. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a lithium niobate micro / nano structure, a dry etching method for forming the structure, and its application.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] In a first aspect, the present invention provides a dry etching method for preparing lithium niobate micro / nano structures, comprising:

[0008] Provide lithium niobate matrix;

[0009] A patterned mask is formed on the surface of the lithium niobate substrate;

[0010] The lithium niobate substrate is etched through the patterned mask using a magnetic neutral loop discharge etching method to form a micro / nano structure;

[0011] During the etching process, the temperature of the lithium niobate substrate is maintained at no less than 400°C, and the etching is performed in an intermittent cyclic manner.

[0012] Secondly, the present invention also provides a lithium niobate micro / nano structure prepared by the above-mentioned dry etching method.

[0013] Thirdly, the present invention also provides the application of the above-mentioned lithium niobate micro / nano structures in the field of nonlinear optics.

[0014] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include at least the following:

[0015] This invention utilizes a magnetic neutral loop discharge etching method to intermittently etch lithium niobate at high temperatures, which can significantly accelerate the reaction rate between fluorine- or chlorine-based gases and lithium niobate, thus greatly increasing the etching rate. During the reaction between lithium niobate and the gas, the products generated are rapidly volatilized due to the high temperature, preventing deposition or adhesion on the lithium niobate surface. This effectively avoids lateral corrosion and greatly improves the etching verticality of the micro / nano structure. High-temperature etching promotes the chemical reaction between the reactive gas and lithium niobate, while the photoresist does not react chemically with the reactive gas but is only subjected to physical bombardment by radio frequency particles. Therefore, under the premise of constant radio frequency power, high-temperature etching can significantly increase the etching rate ratio between lithium niobate and photoresist. This is beneficial in some preferred embodiments where photoresist can be directly used as a mask to prepare lithium niobate micro / nano structures with high aspect ratios, avoiding steps such as preparing metal or dielectric hard masks, greatly simplifying the fabrication process and effectively reducing processing costs.

[0016] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below in conjunction with detailed drawings. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a dry etching method provided in a typical embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of the specific process of the dry etching method provided in a typical embodiment of the present invention;

[0019] Figure 3 This is an electron microscope image of a lithium niobate micro / nano structure prepared by a dry etching method according to a typical embodiment of the present invention;

[0020] Figure 4 This is an electron microscope image of a lithium niobate micro / nano structure prepared by a dry etching method provided in a typical comparative case of the present invention;

[0021] Figure 5 This is an electron microscope image of a lithium niobate micro / nano structure prepared by a dry etching method, provided in another typical comparative case of this invention. Detailed Implementation

[0022] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0024] Moreover, relational terms such as “first” and “second” are used merely to distinguish one component or method step from another that has the same name, and do not necessarily require or imply any such actual relationship or order between these components or method steps.

[0025] Current research indicates that magnetic neutral loop discharge (NLD) etching technology, compared to ICP, can apply a high-frequency electric field to a toroidal magnetic neutral line formed in a vacuum cavity where the magnetic field strength is zero, thereby generating plasma. By changing the current magnitude, the diameter and density of the plasma can be controlled, thus offering advantages such as high etching rate, high uniformity, high plasma density, and low-voltage discharge.

[0026] Researchers have already used NLD (Non-Die Lamination) to etch lithium niobate at room temperature. Although this improved the etching rate and produced micron-scale high aspect ratio structures, the verticality of the structures remained poor. In the fabrication of nanoscale structures, it is still difficult to achieve high aspect ratio etching.

[0027] The inventors discovered through long-term practice that when etching lithium niobate at room temperature (23-40℃) using the aforementioned etching method, some byproducts inevitably form. These byproducts are relatively difficult to volatilize at room temperature and continuously deposit on the surface of the lithium niobate to be etched. This significantly reduces the vertical etching rate, thus prolonging the etching time. Prolonged etching leads to excessive lateral corrosion and the deposition of a large amount of byproducts, drastically reducing the etching selectivity between lithium niobate and the photoresist mask, and adversely affecting the morphology of the lithium niobate micro / nanostructure. This results in poor verticality, low height, and low aspect ratio of the prepared lithium niobate micro / nanostructure. This significantly restricts the market promotion and application of lithium niobate micro / nano optoelectronic devices.

[0028] See Figure 1 To address the aforementioned technical problems, this invention provides a dry etching method for fabricating lithium niobate micro / nano structures, comprising the following steps:

[0029] Provides lithium niobate matrix.

[0030] A patterned mask is formed on the surface of the lithium niobate substrate.

[0031] The lithium niobate substrate is etched through the patterned mask using a magnetic neutral loop discharge etching method to form a micro / nano structure.

[0032] During the etching process, the temperature of the lithium niobate substrate is maintained at no less than 400°C, and the etching is performed in an intermittent cyclic manner.

[0033] The lithium niobate substrate mentioned above includes, for example, a substrate and a lithium niobate thin film formed on the substrate surface. The present invention focuses on how to etch the lithium niobate thin film with high quality, without imposing too many restrictions on the choice of substrate or how to form the lithium niobate thin film. In addition, even if there are other film layers on the surface of the lithium niobate thin film, that is, the lithium niobate thin film is not the outermost layer, as long as the etching depth penetrates through the other film layers to reach the lithium niobate thin film layer, and the same principle is used to achieve high-quality etching, it is still within the scope of implementation of the present invention.

[0034] As a typical application example of the above technical solution, this embodiment of the invention provides a method for etching thin films of lithium niobate micro / nano structures using high-temperature NLD etching, which includes the following main steps:

[0035] Step 1: Clean the surface of lithium niobate.

[0036] Step 2: Apply a high-temperature evaporation coating of a thickening agent to the surface of lithium niobate.

[0037] Step 3: Spin-coat negative photoresist onto the surface of lithium niobate to expose the micro / nano structure patterned area of ​​lithium niobate.

[0038] Step 4: Develop, fix, harden, bake and remove residual photoresist to obtain the photoresist structure mask.

[0039] Step 5: Use high-temperature NLD dry etching cycle multiple times to reach the specified etching depth.

[0040] Step 6: Thoroughly remove residual photoresist from the surface of the lithium niobate structure to obtain a high-quality lithium niobate micro / nano structure.

[0041] In some more specific embodiments, the temperature of the lithium niobate substrate is maintained at 400-500°C during the etching process.

[0042] In some embodiments, the intermittent cyclic etching includes multiple cyclically set etching periods and intermittent periods, wherein the duration of the etching period is no more than 10 minutes and the duration of the intermittent period is no less than 2 minutes.

[0043] Furthermore, in some embodiments, during the etching phase, the temperature of the lithium niobate substrate is controlled at a first temperature, which promotes a full reaction between the lithium niobate material and the reactant gas. During the intermittent phase, the temperature of the lithium niobate substrate is controlled at a second temperature, which promotes the rapid volatilization of the reactants generated in the previous step. The alternation of etching with these two methods can effectively avoid the reaction between the mixed gas and the sidewalls of the lithium niobate structure, reduce the influence of lateral etching, achieve a strong anisotropic etching effect, and thus improve the steepness of the etched structure.

[0044] Wherein, the second temperature is higher than the first temperature;

[0045] In some further embodiments, the first temperature can be 400-450°C, and the second temperature can be 450-500°C.

[0046] This implementation can utilize temperature changes, using higher temperatures during the intermittent period to promote the removal of deposits generated by etching and to activate the etched surface, thereby further improving the etching selectivity, optimizing the etching depth to width ratio, and improving the verticality of the sidewalls.

[0047] Regarding the specific process conditions during etching, in some implementations, the etching atmosphere used in the magnetic neutral loop discharge etching method includes chlorine-based atmospheres and / or fluorine-based atmospheres.

[0048] Regarding the specific atmosphere, in some embodiments, the etching atmosphere includes any one of Cl2 / Ar mixed gas, Cl2 / BCl3 / Ar mixed gas, SF6 / Ar mixed gas, and CF4 / Ar mixed gas. Of course, the choice of atmosphere is not limited to these; any process gas applicable to the NLD etching method and any mixed gas capable of etching lithium niobate is acceptable.

[0049] In some implementations, the antenna RF power of the magnetic neutral loop discharge etching method is 500-2000W, and the bias RF power is 200-1000W.

[0050] The technical advantages of this invention are not only reflected in achieving excellent etching depth and etching perpendicularity, but also in its broad adaptability to patterned mask materials. Most existing etching methods for lithium niobate suffer from similar etching rates for both lithium niobate and soft photoresists. Therefore, during deep etching, the photoresist mask is often damaged prematurely, making it unsuitable for long etching processes and limiting the application of cheaper and simpler photoresist masks. However, this invention overcomes these problems. The change in etching rate caused by high temperature avoids photoresist mask loss during deep etching. Therefore, in some embodiments, the patterned mask can be selected from photoresist masks. It should be noted that selecting a photoresist mask is a preferred embodiment of this invention. If those skilled in the art still choose hard masks, it is still within the scope of this invention, because even with hard masks, improved etching quality can still be achieved.

[0051] Depending on the choice of photoresist mask, in some implementations, the dry etching method specifically includes:

[0052] A photoresist layer is formed by coating the surface of the lithium niobate substrate.

[0053] The patterned mask is formed after exposure, development, and baking.

[0054] Specifically, in some embodiments, the photoresist mask is made of a material selected from hydrogen silsesquioxane polymer photoresist and / or negatively conductive electron beam photoresist. Considering that the present invention intentionally raises the substrate temperature during etching to a higher temperature range, the photoresist used in the present invention is selected from photoresists that are more resistant to high temperatures. Of course, the feasible selection range is not limited to the types mentioned above, and any photoresist that can withstand this temperature range is acceptable.

[0055] Regarding the specific details of the photoresist mask, in some implementations, the thickness of the photoresist layer is 200-1200nm; however, it is not limited to this, and the specific thickness of the photoresist layer can be determined according to the specific etching requirements.

[0056] In some implementations, the exposure method includes, but is not limited to, extreme ultraviolet exposure or electron beam exposure.

[0057] To further improve the etching quality, in some embodiments, the etching method may further include the following steps:

[0058] The steps of cleaning and first plasma treatment of the lithium niobate substrate surface are performed before coating to form the photoresist layer.

[0059] Alternatively, in some implementations, after forming the patterned mask, a second plasma treatment of the exposed area of ​​the patterned mask is further included.

[0060] Alternatively, in some implementations, the process may include a step of removing the patterned mask after the etching process is completed.

[0061] It should be noted that whether or not the surface and exposed areas are cleaned or subjected to plasma treatment, and how the photoresist mask is removed, are not the key factors that determine the etching quality of this invention. Those skilled in the art can adapt or replace the specific cleaning and treatment methods. Any implementation method that can remove impurities, adsorbents or residues can be regarded as an equivalent replacement and is within the scope of implementation of this invention.

[0062] As a specific implementation example of the above technical solution, the lithium niobate micro / nano structure based on high-temperature NLD etching includes the following specific steps:

[0063] Step 1: Clean the surface of lithium niobate using organic ultrasonic cleaning, dry the substrate with nitrogen gas and bake the substrate at high temperature to completely evaporate the moisture on the surface of the lithium niobate film.

[0064] Step 2: The baked substrate is bombarded with oxygen plasma to further remove residual organic matter from the surface. A tackifier is then vapor-coated onto the clean lithium niobate surface at high temperature.

[0065] Step 3: A high-resolution and etch-resistant negative photoresist film is prepared on the surface of lithium niobate using spin coating, and the micro / nano structure patterned areas of lithium niobate are exposed.

[0066] Step 4: After development and fixing, high-temperature baking is performed to form a hard photoresist structure mask that is resistant to etching. The photoresist mask is then bombarded with low-power oxygen plasma to remove residual substrate.

[0067] Step 5: Use high-temperature NLD dry etching cycle multiple times to reach the specified etching depth.

[0068] Step 6: After organic ultrasonic cleaning, high-power oxygen plasma bombardment thoroughly removes residual photoresist, obtaining high-quality lithium niobate micro / nano structures.

[0069] More specifically, in step 1, the lithium niobate material includes, but is not limited to, lithium niobate wafers, silicon-based thin-film lithium niobate, and silicon oxide-based thin-film lithium niobate. Surface cleaning includes the removal of organic matter and surface heat treatment, specifically by ultrasonic cleaning with acetone, isopropanol, and deionized water for 20 minutes each, drying with nitrogen, and then baking on a hot plate at 130°C for 120 seconds.

[0070] In step 2, for example, a high-power (400W) oxygen plasma can be used to treat the surface of lithium niobate for 10 minutes to fully react and decompose the residual organic matter on the surface. A layer of tackifier can then be applied to the surface of lithium niobate using a vapor coating method to improve the coating quality.

[0071] In step 3, the high-resolution, etch-resistant negative photoresist material spin-coated includes, but is not limited to, hydrogen silsesquioxane polymers (HSQ), negative conductive electron beam photoresist, and the spin-coating speed includes, but is not limited to, 1000-4000 rpm, the photoresist thickness includes, but is not limited to, 200-1200 nm, and after spin-coating, it is placed on a hot plate at 180°C and baked for 10-30 minutes; the exposure method used includes, but is not limited to, extreme ultraviolet (EUV) lithography and electron beam (EBL) lithography.

[0072] In step 4, after development and fixing, the substrate needs to be placed in a 180°C oven for 30 minutes to bake the hard film so that the moisture in the photoresist can be completely evaporated and an etch-resistant photoresist structure mask can be obtained; a low-power (200W) oxygen plasma is used to treat the area for 2 minutes to completely remove the residual photoresist on the lithium niobate to be etched.

[0073] In step 5, the lithium niobate micro / nano structure is etched using NLD dry etching with gases including but not limited to chlorine-based and fluorine-based gases. The etching gases include but are not limited to mixed gases of Cl2 / Ar, Cl2 / BCl3 / Ar, SF6 / Ar, and CF4 / Ar. The antenna RF power range is 500-2000W, the bias RF power range is 200-1000W, and the etching tray temperature is 400-500℃.

[0074] In step 5, the etching time for each lithium niobate micro / nano structure does not exceed 10 minutes, and the cycle is repeated multiple times to reach the specified etching depth, with a cycle interval of 2 minutes.

[0075] In step 6, after the lithium niobate micro / nano structure is etched, residual photoresist is thoroughly removed by organic ultrasonic cleaning and high-power (400W) oxygen plasma treatment (10 minutes) to obtain a high-quality lithium niobate micro / nano structure.

[0076] Corresponding to the above-described dry etching method, this invention also provides lithium niobate micro / nanostructures prepared by the aforementioned dry etching method. These micro / nanostructures are not limited to the preparation of nanopillars or deep nanopores.

[0077] Regarding the size characteristics of the micro / nano structure, in some embodiments, the depth or height of the lithium niobate micro / nano structure is not less than 0.6 μm, and / or the width is not greater than 0.12 μm.

[0078] In some implementations, the aspect ratio or height-to-width ratio of the lithium niobate micro / nano structure is not less than 5:1.

[0079] In some implementations, the sidewall verticality of the lithium niobate micro / nanostructure is not less than 88°.

[0080] Furthermore, embodiments of the present invention also provide the application of the above-mentioned lithium niobate micro / nano structures in the field of optical device fabrication.

[0081] Specific applications include, for example, the low-cost, high-efficiency etching method for preparing lithium niobate micro / nano structures with high aspect ratio and high verticality provided by this invention, which can be used to realize lithium niobate photonic chips, optical storage devices, nonlinear optical devices, and optoelectronic modulation devices.

[0082] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0083] Example 1

[0084] This embodiment provides a method for high-temperature NLD dry etching of lithium niobate micro / nano structures, specifically including the following steps:

[0085] Step 1: Prepare the lithium niobate material and clean its surface. First, rinse the surface of the lithium niobate material with plenty of flowing deionized water. Then, immerse it sequentially in acetone, isopropanol, and deionized water for ultrasonic cleaning, repeating the ultrasonic treatment twice for 10-30 minutes in each solution. Next, use nitrogen to dry the water stains on the lithium niobate material and bake it on a 130°C hot plate for 180 seconds to completely evaporate any remaining moisture. Finally, place it in an oxygen plasma degumming machine and bombard the surface of the lithium niobate with high-power (400W) oxygen plasma for 20 minutes to completely react and volatilize any residual organic matter on the surface, thus obtaining a clean lithium niobate material.

[0086] Step 2: Place the cleaned lithium niobate material described in Step 1 into a high-temperature evaporation coating equipment and evaporate the tackifier at 150°C for 5 minutes to improve the adhesion between the photoresist and the lithium niobate surface, thereby enhancing the thickness and uniformity of the photoresist coating.

[0087] Step 3: A high-resolution, etch-resistant negative photoresist is prepared on the lithium niobate surface coated with the tackifier described in Step 2 using a spin coating method. The high-resolution, etch-resistant negative photoresist material is hydrogen silsesquioxane polymers (HSQ). The spin coating speed is 3000 rpm, and the photoresist thickness is about 600 nm. After spin coating, the photoresist is placed on a hot plate at 180°C and baked for 10 minutes.

[0088] Step 4: Place the substrate coated with photoresist described in Step 3 into a photolithography machine to pattern the lithium niobate micro / nano structure region. The exposure method used is electron beam lithography (EBL).

[0089] Step 5: Remove the substrate after patterning exposure as described in Step 4 and perform development and fixing. The required developer is TMAH developer and a mixture of 4-methyl-2-pentanone and isopropanol in a ratio of 1:3, with a development time of 120 seconds. The required fixer is deionized water and isopropanol, with a fixing time of 30 seconds. Finally, use nitrogen to dry the residual solution on the substrate and place the substrate in a 180°C oven for hardening and baking for 30 minutes to completely evaporate the moisture in the photoresist and obtain an etch-resistant photoresist structure mask. Use low-power (200W) oxygen plasma to treat for 2 minutes to completely remove the residual photoresist on the lithium niobate area to be etched.

[0090] Step 6: Place the substrate carrying the photoresist mask described in Step 5 into the NLD etching system, set the etching tray temperature to 400℃, and when the temperature reaches the required level, set the antenna RF power range to 1200W and the bias RF power range to 800W. Use chlorine-based gas NLD dry etching, with the etching gas including a mixture of Cl2 / BCl3 / Ar = 7:4:1 to etch lithium niobate. Each etching session lasts 8 minutes, with a 2-minute interval, and the etching is repeated multiple times to reach the specified depth.

[0091] Step 7: After etching the lithium niobate micro / nano structure, organic ultrasonic cleaning and high-power (400W) oxygen plasma treatment (10 minutes) are used to thoroughly remove residual photoresist to obtain a high-quality lithium niobate micro / nano structure.

[0092] Comparative Example 1

[0093] This comparative example is largely the same as Example 1, with the only difference being:

[0094] In step 6, the lithium niobate substrate is not heated during etching; instead, it is etched directly at room temperature in the laboratory.

[0095] Figure 2 The diagram illustrates the specific process of the etching methods performed in the above embodiments and comparative examples. Figures (a) and (b) represent the mask preparation process. As shown in figure (c), in the prior art, when etching lithium niobate in a room temperature (23-40℃) environment, byproducts inevitably form. These byproducts are relatively difficult to volatilize at room temperature and continuously deposit on the surface of the lithium niobate to be etched. This significantly reduces the etching rate, thereby prolonging the etching time. Prolonged etching leads to excessive lateral corrosion and the deposition of a large amount of byproducts, drastically reducing the etching selectivity between lithium niobate and the photoresist mask, and adversely affecting the morphology of the lithium niobate micro / nanostructure. This results in poor verticality, low height, and low aspect ratio of the prepared lithium niobate micro / nanostructure.

[0096] Conversely, as shown in inset (c1), etching lithium niobate in a high-temperature environment promotes the chemical reaction between the mixed gas and the lithium niobate material. More importantly, the reaction products are highly volatile at high temperatures and hardly adhere to the lithium niobate surface. This increases the contact area between the lithium niobate material and the reactant gas, thereby significantly improving the etching rate of lithium niobate. The photoresist, however, does not react chemically with the mixed gas and is only subjected to physical bombardment by the plasma. The effect of high temperature on the etching rate of the photoresist is negligible, ultimately resulting in a high selectivity etching effect. Due to the short etching time, severe lateral corrosion does not occur. High verticality and high aspect ratio lithium niobate micro / nano structures can be fabricated.

[0097] Figure 3 The scanning electron microscope image of the prepared lithium niobate micro / nano structure shows that the sidewalls of the prepared lithium niobate micro / nano structure are vertical and smooth, with a verticality of up to 88° and a depth-to-width ratio of up to 5:1.

[0098] Comparative Example 2

[0099] This comparative example is largely the same as Example 1, with the only difference being:

[0100] In step 6, the etching is not interrupted, but is performed continuously for the same total etching time.

[0101] Ultimately Figure 4 As shown, the aspect ratio of the prepared microstructure can only reach 3:1, and the verticality of the sidewalls is only 70°. Furthermore, the sidewalls of the structure are very rough, and the bottom of the structure is stuck together and cannot be separated. The etching quality is significantly weaker than that of Example 1.

[0102] Comparative Example 3

[0103] This comparative example is largely the same as Example 1, with the only difference being:

[0104] In step 6, the etching temperature is 200°C, and the etching is performed intermittently.

[0105] Ultimately Figure 5 As shown, the aspect ratio of the prepared microstructure can only reach 1:1, and the verticality of the sidewalls is only 60°, with the etching quality being significantly weaker than that of Example 1.

[0106] Furthermore, in numerous experiments concerning temperature, the inventors of this invention discovered that when the temperature is below the critical value, it is often difficult to obtain superior etching quality. Typically, the temperature needs to be above the temperature specified in the technical solution of this invention to achieve a significant improvement in etching quality more suddenly. Moreover, this improvement can only be achieved by combining intermittent cyclic etching, and neither can be omitted.

[0107] Example 2

[0108] This embodiment is largely the same as Embodiment 1, with the main difference being:

[0109] In step 6, the tray temperature is set to 425°C during the etching phase and 475°C during the intermittent phase.

[0110] After testing, the prepared lithium niobate micro / nano structure has a smooth, vertical sidewall with a verticality of 88.5-89° and a maximum depth-to-width ratio of 7:1.

[0111] Example 3

[0112] This embodiment is largely the same as Embodiment 1, with the main difference being:

[0113] In step 3, the photoresist used is ultraviolet photoresist, the spin coating speed is 2000 rpm, the photoresist layer thickness is 600 nm, and the baking time is 10 minutes.

[0114] In step 4, the exposure method used is extreme ultraviolet exposure.

[0115] In step 6, the etching tray temperature is set to 450℃. When the temperature reaches the required level, the antenna RF power is set to 2000W and the bias RF power is set to 200W. Fluorine-based gas NLD dry etching is used, and the etching gas is a mixture of SF6 and Ar in a ratio of 5:1. Each etching session lasts 10 minutes, with a 2-minute interval between each session. This etching process is repeated multiple times to achieve the specified depth.

[0116] Example 4

[0117] This embodiment is largely the same as Embodiment 1, with the main difference being:

[0118] In step 3, the photoresist used is SU-8 photoresist, the spin coating speed is 4000 rpm, the photoresist layer thickness is 1200 nm, and the baking time is 15 minutes.

[0119] In step 4, the exposure method used is laser direct writing exposure.

[0120] In step 6, the etching tray temperature is set to 500℃. When the temperature reaches the required level, the antenna RF power is set to 500W and the bias RF power is set to 1000W. Chlorine-based gas NLD dry etching is used, and the etching gas is a mixture of Cl2 and Ar in a ratio of 6:1. Each etching session lasts 5 minutes, with a 2-minute interval between each session. This etching process is repeated multiple times to achieve the specified depth.

[0121] Both of the above embodiments 3 and 4 can achieve excellent aspect ratio and excellent sidewall verticality, and are in a very similar range to embodiment 1.

[0122] Based on the above test results, it can be clearly stated that (1) the present invention uses the NLD system to etch lithium niobate at high temperature, which can greatly promote the reaction rate between fluorine-based or chlorine-based gas and lithium niobate, and significantly accelerate the etching rate.

[0123] (2) In the embodiments of the present invention, the products generated during the reaction of lithium niobate with gas will be rapidly volatilized by high temperature and will not be deposited or attached to the surface of lithium niobate. This effectively avoids the occurrence of lateral corrosion and greatly improves the etching verticality of micro-nano structures.

[0124] (3) In this embodiment of the invention, high-temperature etching promotes the chemical reaction between the reactive gas and lithium niobate, while the photoresist does not react chemically with the reactive gas and is only subjected to physical bombardment by radio frequency particles. Therefore, under the premise of unchanged radio frequency power, high-temperature etching can significantly increase the etching rate ratio between lithium niobate and photoresist, which is beneficial to directly use photoresist as a mask to prepare lithium niobate micro-nano structures with high aspect ratio. At the same time, it avoids the steps of preparing metal or dielectric hard masks, greatly simplifies the preparation process, and effectively reduces the processing cost.

[0125] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A dry etching method for preparing lithium niobate micro / nano structures, characterized in that, include: Provide lithium niobate matrix; A patterned mask is formed on the surface of the lithium niobate substrate; The lithium niobate substrate is etched through the patterned mask using a magnetic neutral loop discharge etching method to form a micro / nano structure; During the etching process, the temperature of the lithium niobate substrate is maintained at 400-500°C, and the etching is performed in an intermittent cyclic manner. The intermittent cyclic etching includes multiple cyclic etching periods and intermittent periods. The duration of each etching period is no more than 10 minutes, and the duration of each intermittent period is no less than 2 minutes.

2. The dry etching method according to claim 1, characterized in that, During the etching period, the temperature of the lithium niobate substrate is controlled at a first temperature, and during the intermittent period, the temperature of the lithium niobate substrate is controlled at a second temperature; the second temperature is higher than the first temperature; the first temperature is 400-450℃, and the second temperature is 450-500℃.

3. The dry etching method according to claim 1, characterized in that, The etching atmosphere used in the magnetic neutral loop discharge etching method includes chlorine-based atmosphere or fluorine-based atmosphere.

4. The dry etching method according to claim 3, characterized in that, The etching atmosphere includes any one of Cl2 / Ar mixed gas, Cl2 / BCl3 / Ar mixed gas, SF6 / Ar mixed gas, and CF4 / Ar mixed gas; And / or, the antenna RF power of the magnetic neutral loop discharge etching method is 500-2000W, and the bias RF power is 200-1000W.

5. The dry etching method according to claim 1, characterized in that, The patterned mask is selected from a photoresist mask; The dry etching method specifically includes: A photoresist layer is coated onto the surface of the lithium niobate substrate; The patterned mask is formed after exposure, development, and baking.

6. The dry etching method according to claim 5, characterized in that, The photoresist mask is made of a material selected from hydrogen silsesquioxane polymer photoresist or negative conductive electron beam photoresist. And / or, the thickness of the photoresist layer is 200-1200 nm; And / or, the exposure method includes either extreme ultraviolet exposure or electron beam exposure.

7. The dry etching method according to claim 5, characterized in that, Also includes: Before coating to form the photoresist layer, the lithium niobate substrate surface is cleaned and subjected to a first plasma treatment. And / or, after forming the patterned mask, a step of performing a second plasma treatment on the exposed area of ​​the patterned mask; And / or, after the etching process is completed, the step of removing the patterned mask.

8. The lithium niobate micro / nano structure prepared by the dry etching method according to any one of claims 1-7, wherein the lithium niobate micro / nano structure has a depth or height of not less than 0.6 μm, a width of not more than 0.12 μm, a depth-to-width ratio or height-to-width ratio of not less than 5:1, and a sidewall verticality of not less than 88°.

9. The application of the lithium niobate micro / nano structure according to claim 8 in the fields of integrated photonic devices, optoelectronic modulation devices, and waveguide mode sensor devices.

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