Design, preparation and application of extreme ultraviolet zone plates

Abstract

The present invention provides a method for designing a zone plate for focusing in the extreme ultraviolet band, comprising: determining a preset object distance p; determining a preset image distance q; determining an extreme ultraviolet wavelength λ; and obtaining the radius r of the nth zone according to the following formula when the value of p+q is less than 750nλ and the value of q is less than 50nλ. n : When the value of p+q is greater than or equal to 750nλ and the value of p+q is greater than or equal to 50nλ, the radius of the nth ring zone r is obtained according to the following formula n :According to r n The radii of each zone of the EUV zone plate are designed based on the preset diameter and outermost ring width of the EUV zone plate, as well as the radii of each zone. The zone plate designed using the method of the present invention has higher diffraction efficiency and imaging quality by establishing two judgment conditions.

Description

Technical Field

[0001] The present invention relates to the field of synchrotron radiation focusing elements, and in particular to the design, preparation method and application of an extreme ultraviolet zone plate. Background Art

[0002] Nanoprobe technology is an important way to achieve high-resolution characterization using synchrotron radiation and is widely used in materials, physics, biology, medicine and other fields. Focusing optical elements are a crucial component in nanoprobe technology, directly affecting spatial resolution and imaging quality. To achieve higher-resolution imaging, the light spot must usually be focused to less than 100 nanometers, which also places higher demands on the focusing elements. Zone plate focusing is the preferred method for achieving light spots less than 100 nanometers. The focused spot size is comparable to the width of the outermost ring and can reach tens of nanometers.

[0003] However, in the extreme ultraviolet band, that is, the wavelength range of 10nm-121nm, the diffraction efficiency of high-resolution Fresnel zone plates is far lower than the theoretical diffraction efficiency. During actual imaging, artifacts such as aberrations will be generated, affecting the imaging quality, which has not yet been effectively solved. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above-mentioned technical problems, the present invention provides a design method of an extreme ultraviolet zone plate, which includes:

[0005] Determine a preset object distance p; determine a preset image distance q; determine an extreme ultraviolet wavelength λ;

[0006] When the value of p+q is less than 750nλ, the radius of the nth ring zone r is obtained according to formula (1): n :

[0007]

[0008] At values ​​of p+q greater than or equal to 750nλ and When the value of is less than 50nλ, the radius of the nth ring zone r is obtained according to formula (2): n :

[0009]

[0010] At values ​​of p+q greater than or equal to 750nλ and When the value of is greater than or equal to 50nλ, the radius of the nth ring zone r is obtained according to formula (3): n :

[0011]

[0012] According to r nThe extreme ultraviolet zone plate is designed according to the preset diameter and outermost ring width of the extreme ultraviolet zone plate and the radius of each ring zone.

[0013] A second aspect of the present invention discloses a method for preparing an extreme ultraviolet zone plate, comprising:

[0014] Determine the photolithography pattern of the extreme ultraviolet zone plate according to the above design method;

[0015] Spin coating hydrogen silsesquioxane on a silicon nitride window, wherein the silicon nitride window has a silicon wafer as a supporting substrate;

[0016] exposing the silicon nitride window spin-coated with hydrogen silsesquioxane photoresist using an electron beam lithography machine according to the photolithography pattern, wherein the hydrogen silsesquioxane photoresist forms amorphous silicon dioxide under electron beam irradiation;

[0017] placing the exposed silicon nitride window in a developer for development;

[0018] The developed silicon nitride window is dried to obtain an extreme ultraviolet zone plate.

[0019] According to an embodiment of the present invention, placing the exposed silicon nitride window in a developer for development includes:

[0020] The exposed silicon nitride window was placed in 25% by mass tetramethylammonium hydroxide for 55 to 65 seconds for development and fixed in water for 25 to 35 seconds;

[0021] The fixed silicon nitride window was placed in isopropyl alcohol and allowed to stand for 4 to 6 minutes.

[0022] According to an embodiment of the present invention, it is preferred that the film is placed in 25% by mass tetramethylammonium hydroxide for development for 60 seconds, fixed in water for 30 seconds, and then placed in isopropyl alcohol for 5 minutes.

[0023] According to an embodiment of the present invention, the thickness of the hydrogen silsesquioxane photoresist spin-coated on the silicon nitride window is 60 nm.

[0024] According to an embodiment of the present invention, the method further comprises spin coating hydrogen silsesquioxane photoresist on the silicon nitride window and then baking the photoresist on a hot plate at 80-100° C. for 3-8 minutes.

[0025] According to an embodiment of the present invention, drying the developed silicon nitride window includes blowing the developed silicon nitride window dry with an air gun.

[0026] The third aspect of the present invention discloses an extreme ultraviolet zone plate prepared by the above preparation method.

[0027] A fourth aspect of the present invention discloses an application of the above-mentioned extreme ultraviolet zone plate in synchrotron radiation probe technology.

[0028] According to an embodiment of the present invention, the above-mentioned EUV zone plate is used to focus light in the EUV band into a light spot smaller than 100 nm.

[0029] According to an embodiment of the present invention, a design concept for extreme ultraviolet zone plates used in synchrotron radiation is provided, which can design the ring zone radii of high-efficiency large-diameter zone plates in the extreme ultraviolet band, improve the traditional design method based on paraxial approximation, and establish two judgment conditions: the value of p+q is less than the value of 750nλ and The value of is less than 50nλ and the corresponding different formulas are used to design the annular zone radius, so that the designed wave zone plate has higher diffraction efficiency and imaging quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0031] Figure 1 Schematic diagram of the optical path of the nth zone of the zone plate according to an embodiment of the present invention;

[0032] Figure 2 This is a flow chart of a method for preparing an extreme ultraviolet zone plate according to an embodiment of the present invention;

[0033] Figure 3 This is a flow chart of the preparation process of an extreme ultraviolet zone plate according to an embodiment of the present invention;

[0034] Figure 4 Comparison diagram of focusing a 100 eV extreme ultraviolet light spot 4.839 mm away to a spot 4.839 mm according to an embodiment of the present invention; (a) is the design method of embodiment 1; (b) is the design method of comparative example 1; (c) is the design method of comparative example 2;

[0035] Figure 5 This is a comparison chart of diffraction efficiency when focusing a 100eV extreme ultraviolet light spot 4.839mm away to 4.839mm according to an embodiment of the present invention;

[0036] Figure 6 Comparison diagram of focusing a 100 eV extreme ultraviolet light spot from 2419 mm away to a spot size of 2.422 mm according to an embodiment of the present invention; (a) is the design method of Example 2; (b) is the design method of Comparative Example 3; (c) is the design method of Comparative Example 4;

[0037] Figure 7 This is a comparison chart of diffraction efficiency when focusing a 100eV extreme ultraviolet light spot 2419mm away to 2.422mm according to an embodiment of the present invention. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0039] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concept of the present invention.

[0040] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise," "include," etc. used herein indicate the presence of features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0041] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0042] When expressions such as “at least one of A, B, and C, etc.” are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (e.g., “a system having at least one of A, B, and C” should include but is not limited to systems having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, and C, etc.). When expressions such as “at least one of A, B, or C, etc.” are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (e.g., “a system having at least one of A, B, or C” should include but is not limited to systems having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, and C, etc.).

[0043] Characterization techniques using nanoprobes include scanning transmission X-ray microscopy (STXM), X-ray fluorescence (XRF), ptychography, and nano-angle-resolved photoelectron spectroscopy (Nano-ARPES). Current synchrotron radiation probe technologies use a variety of focusing elements, such as Kirkpatrick-Baez (KB) mirrors, capillary focusing lenses, and metal zone plates.

[0044] In the process of realizing the conception of the present invention, it is found that the radius of the nth ring can be r n = The calculation formula is used to design the extreme ultraviolet zone plate, where λ and f are the designed working wavelength and focal length of the zone plate respectively. Then, after calculating the radius of each ring zone of the zone plate, the zone plate photolithography pattern is designed. The amplitude type zone plate achieves diffraction enhancement of the light field by blocking the anti-phase light field. According to optical theory, its theoretical diffraction efficiency is 1 / π 2 .

[0045] However, with the development of zone plate processing technology, the diameter of the zone plate has become larger and larger, the width of the outermost ring has become smaller and smaller, and the number of ring zones has increased significantly. The traditional Fresnel zone plate formula is no longer applicable. Especially in the extreme ultraviolet band, the processed zone plate cannot effectively block the reverse light field, so its diffraction efficiency has dropped significantly. The existing large-diameter zone plates have low focusing efficiency and cannot meet the requirements of synchrotron radiation nanoprobe technology. In order to improve the focusing efficiency of zone plates in the extreme ultraviolet band, it is necessary to further develop a high-efficiency focusing zone plate that can achieve higher diffraction efficiency and imaging quality.

[0046] According to an embodiment of the present invention, a method for designing an extreme ultraviolet zone plate is provided, comprising:

[0047] Determine a preset object distance p;

[0048] Determine the preset image distance q;

[0049] Determine the extreme ultraviolet wavelength λ;

[0050] When the value of p+q is less than 750nλ, the radius of the nth ring zone r is obtained according to formula (1): n :

[0051]

[0052] At values ​​of p+q greater than or equal to 750nλ and When the value of is less than 50nλ, the radius of the nth ring zone r is obtained according to formula (2): n :

[0053]

[0054] At values ​​of p+q greater than or equal to 750nλ and When the value of is greater than or equal to 50nλ, the radius of the nth ring zone r is obtained according to formula (3): n :

[0055]

[0056] According to r n The radius of each zone of the EUV zone plate is designed based on the value;

[0057] The extreme ultraviolet zone plate is designed according to the preset diameter and outermost ring width of the extreme ultraviolet zone plate, as well as the radius of each ring zone.

[0058] During the implementation of this invention, it was discovered that the diffraction efficiency of high-resolution Fresnel zone plates in the extreme ultraviolet (EUV) band is far lower than the theoretical diffraction efficiency. This is because the conventional Fresnel zone plate formula is based on a paraxial approximation, which ignores high-order minima derived from the product of wavelength and the number of zones. As the zone plate diameter increases beyond a certain point, good coherence enhancement is no longer achieved, resulting in a decrease in diffraction efficiency. This efficiency reduction is particularly pronounced in the EUV band. Furthermore, as the zone plate diameter increases and the number of zones increases, each transparent zone has different imaging positions, which can produce artifacts such as aberrations and affect image quality.

[0059] Combine Figure 1 The optical path diagram of the nth zone of a zone plate is shown in Figure 1, where p is the object distance and q is the image distance. Based on the Fermat principle and the physical model of coherence enhancement, a strict calculation formula for the zone radius of the zone plate is established. According to the principle of the zone plate, the optical path difference between the light passing through its nth zone and the light along the optical axis is n times of half a wavelength. Therefore, the following formula (4) can be obtained:

[0060]

[0061] Squaring and simplifying the two equations on the right side of the above equation yields the following equation, equation (1):

[0062]

[0063] When p+q>>nλ / 2, the above formula is simplified to the following formula (2):

[0064]

[0065] when When , formula (2) is simplified to the following formula (5):

[0066]

[0067] When p+q>>nλ / 2 and When both are satisfied, it can be further simplified to the following formula (3):

[0068]

[0069] The zone plate can be regarded as a special lens, whose focal length f, object distance p and image distance q satisfy Right now From (5) we can get This is the current common design formula for zone plates. Equation (2) is an accurate formula when the illumination light is parallel. However, when p + q >> nλ / 2 is not satisfied, the zone plate ring design formula needs to be further modified to (1), which is the accurate calculation formula for the zone plate ring radius.

[0070] Bundle Substituting into formula (1) yields the following formula (6):

[0071]

[0072] According to an embodiment of the present invention, the traditional zone plate design formula, i.e., formula (3), cannot achieve good coherence enhancement under the condition of a large number of rings, so the diffraction efficiency decreases. Especially in the extreme ultraviolet band, the efficiency decreases significantly; and the traditional zone plate design formula, i.e., formula (3), ignores the high-order small quantities of the product of the wavelength and the number of rings. However, in the actual imaging of the extreme ultraviolet band and the zone plate with a large number of rings, each transparent ring zone has a different imaging position, which will produce artifacts such as aberrations. Therefore, it is not possible to use the simplified formula (3) without considering the extreme ultraviolet band and the large number of rings. In the process of designing the zone plate, those skilled in the art often ignore that formula (3) is obtained by ignoring the high-order small quantities of the product of the wavelength and the number of rings. When the designed zone plate has low diffraction efficiency and poor imaging quality, they will not consider the problem caused by the inaccuracy of the original design formula. Therefore, the present invention uses the precise formula, i.e., formula (1), to design the zone plate and the value of nλ / 2 when the value of p+q is less than 1500 times and The value of is less than 200 times the value of nλ / 4, that is, the value of p+q is less than 750nλ and When the value of is less than 50nλ, the accurate calculation formula of high-order small quantities without neglecting the product of wavelength and number of zones is used, i.e., formula (1). When the above conditions are not met, the zone plate designed using the traditional formula, i.e., formula (3), can achieve similar diffraction efficiency and imaging quality. When the value of p+q is less than 750nλ, it is no longer necessary to consider The value of p+q is greater than or equal to 750nλ, and the zone plate is designed directly using formula (1). The value of When the value is less than 50nλ, use formula (2) to When the value is greater than or equal to 50nλ, using formula (3) and the above design method, the coherence enhancement of efficiency can be achieved and the aberration can be overcome.

[0073] In some embodiments of the present invention, the value of p+q is greater than 750nλ but does not satisfy When the value of is greater than 50nλ, the diffraction efficiency of the zone plate designed using formula (2) is close to that of formula (1), but both are higher than the diffraction efficiency using the simplified formula (3) commonly used in this field.

[0074] In some embodiments of the present invention, it can be seen from formula (6) that even if λf is a certain value, r n The product of the object distance and the image distance and Therefore, the above-mentioned zone plate zone radius design formula is applicable to focusing or imaging with fixed object distance and image distance.

[0075] According to an embodiment of the present invention, a method for preparing an extreme ultraviolet zone plate is provided, the process is as follows: Figure 2 As shown in the process flow chart Figure 3 As shown, the following steps S1 to S5 are included:

[0076] Step S1: Determine the photolithography layout of the EUV zone plate according to the above design method.

[0077] Step S2: Spin-coating hydrogen silsesquioxane photoresist (HSQ) on the silicon nitride window, wherein the silicon nitride window has a silicon wafer as a supporting substrate, such as Figure 3 As shown in (a) and (b).

[0078] Step S3: Expose the silicon nitride window with hydrogen silsesquioxane photoresist spin-coated thereon using an electron beam lithography machine according to the photolithography pattern, wherein the hydrogen silsesquioxane photoresist forms amorphous silicon dioxide under electron beam irradiation. Figure 3 As shown in (c).

[0079] Step S4: placing the exposed silicon nitride window in a developer for development.

[0080] Step S5: Dry the developed silicon nitride window to obtain an EUV zone plate such as Figure 3 As shown in (d) in .

[0081] According to an embodiment of the present invention, a conventional zone plate is manufactured by electron beam lithography combined with electroplating, which requires a two-step process. The large-diameter zone plate designed for the above-mentioned design method uses the photoresist pattern obtained after lithography to directly perform imaging, and no longer performs electroplating to transfer the pattern, which can simplify the process flow, reduce process complexity, make the production process more concise, and at the same time reduce production costs, eliminate the materials and equipment required for electroplating, and the equipment maintenance and operating costs caused by the complex process; direct imaging can reduce pattern deformation or distortion caused by the electroplating process, thereby obtaining a more accurate zone plate pattern; the electroplating process may involve the use of harmful chemicals and wastewater treatment problems, and omitting the electroplating step helps reduce environmental pollution; the simplified process flow helps improve the consistency of the production process, reduce the quality fluctuations caused by the multi-step process, and make the prepared zone plate have higher precision, better conform to the design layout, and thus have higher diffraction efficiency and imaging quality.

[0082] According to an embodiment of the present invention, in step S2 , the hydrogen silsesquioxane photoresist is spin-coated on the silicon nitride window to a thickness of 60 nm.

[0083] In some specific embodiments of the present invention, the model of the HSQ photoresist is HSQ 1541-002.

[0084] In some specific embodiments of the present invention, in step S2, the silicon nitride window having a silicon wafer as a supporting substrate includes: a 200μm thick silicon wafer as a supporting substrate, a 50nm thick silicon nitride film grown on the silicon wafer, and a square window with a size of 1.5mm in the middle of the silicon wafer for preparing a wave zone plate.

[0085] According to an embodiment of the present invention, after step S2, the process further includes spin coating hydrogen silsesquioxane photoresist on the silicon nitride window and then baking on a hot plate at 80-100° C. for 3-8 minutes.

[0086] According to an embodiment of the present invention, pre-baking can remove the solvent in the photoresist, ensure the uniformity and consistency of the photoresist layer, and can also enhance the adhesion between the photoresist and the substrate, reducing peeling or falling off during the development process. The pre-baking time can be 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, or 8 minutes, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable. A pre-baking time of 3 to 8 minutes can ensure that the solvent in the photoresist is effectively removed without overheating the photoresist, thereby avoiding excessive flow or deformation of the material. If the pre-baking time is too short, the solvent in the photoresist may not be completely removed, resulting in an uneven photoresist layer, affecting subsequent exposure and development effects. If the pre-baking time is too long, the photoresist layer may be over-cured or thermally degraded, affecting the performance of the photoresist and the accuracy of the pattern.

[0087] In some embodiments of the present invention, the HSQ photoresist may be spin-coated and then pre-baked on a hot plate at 100°C. The baking temperature may be 80°C, 90°C, or 100°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0088] In some embodiments of the present invention, in step S3, the electron beam lithography machine uses JEOL-6300FS to perform exposure based on the calculated annular zone position.

[0089] According to an embodiment of the present invention, step S4 further includes steps S401 to S402:

[0090] Step S401: Place the exposed silicon nitride window in 25% by mass tetramethylammonium hydroxide for development for 55 to 65 seconds, and fix it in water for 25 to 35 seconds;

[0091] Step S402: placing the fixed silicon nitride window in isopropyl alcohol and letting it stand for 4 to 6 minutes.

[0092] According to an embodiment of the present invention, in step S401, the silicon nitride window is placed in 25% by mass tetramethylammonium hydroxide. The developing time can be 55 seconds, 56 seconds, 57 seconds, 58 seconds, 59 seconds, 60 seconds, 61 seconds, 62 seconds, 63 seconds, 64 seconds, or 65 seconds, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable. The fixing time in water can be 25 seconds, 26 seconds, 27 seconds, 28 seconds, 29 seconds, 30 seconds, 31 seconds, 32 seconds, 33 seconds, 34 seconds, or 35 seconds, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0093] According to an embodiment of the present invention, in step S401, it is more preferred that the film is placed in 25% by mass tetramethylammonium hydroxide for development for 60 seconds, fixed in water for 30 seconds, and placed in isopropyl alcohol for 5 minutes.

[0094] According to an embodiment of the present invention, after photolithography, the unexposed areas of the negative photoresist hydrogen silsesquioxane photoresist will dissolve, while the photoresist in the exposed areas will be modified into silicon dioxide (SiO2) under electron beam irradiation and retained to form a pattern. The use of 25% by mass tetramethylammonium hydroxide for development can dissolve the residual photoresist in the unexposed areas, and fixing is to remove the residual chemical components and impurities in the development process to ensure the stability of the pattern.

[0095] According to an embodiment of the present invention, in step S402, the standing time in isopropyl alcohol can be 4 minutes, 5 minutes, or 6 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0096] According to an embodiment of the present invention, isopropyl alcohol is a volatile solvent that can evaporate quickly, which helps to remove moisture from the substrate and achieve drying; isopropyl alcohol can also be used to further clean the surface of the substrate, remove possible residues, and improve the surface quality of the substrate; the use of isopropyl alcohol can help stabilize the photoresist pattern and prevent deformation during the drying process.

[0097] According to an embodiment of the present invention, in step S5 , drying the developed silicon nitride window includes: carefully blowing the developed silicon nitride window dry using an air gun.

[0098] According to an embodiment of the present invention, there is provided an extreme ultraviolet zone plate prepared according to the preparation method of steps S1 to S5 above.

[0099] According to an embodiment of the present invention, the zone plate prepared using the above method can be used in nanoprobe technology in the field of synchrotron radiation as a focusing element, and can achieve coherent enhancement of efficiency, improve the diffraction efficiency of the zone plate, and at the same time, the imaging position of each transparent annular zone is closer, reducing artifacts such as aberrations and improving the imaging quality of the zone plate.

[0100] According to an embodiment of the present invention, there is provided an application of the above-mentioned extreme ultraviolet zone plate in synchrotron radiation probe technology.

[0101] According to an embodiment of the present invention, the zone plate is used to focus light in the extreme ultraviolet band into a light spot smaller than 100 nm.

[0102] According to an embodiment of the present invention, in the field of nanoprobe technology of synchrotron radiation, zone plate focusing is the preferred method for achieving light spots below 100 nanometers. The focused light spot size is equivalent to the width of the outermost ring and can reach tens of nanometers. Using the above-mentioned zone plate for focusing, it is possible to focus light in the extreme ultraviolet band, i.e., light with a wavelength of 10nm to 121nm, and obtain a focused light spot less than 100nm or less than 50nm, 30nm or even smaller, thereby achieving higher spatial resolution; at the same time, it has higher diffraction efficiency, improves the signal-to-noise ratio, and achieves fast and efficient characterization.

[0103] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0104] Example 1 Calculation of diffraction efficiency of extreme ultraviolet zone plate

[0105] The design method of the present invention is used to calculate the diffraction efficiency of focusing a 100 eV extreme ultraviolet light spot 4.839 mm away to 4.839 mm with an 8333 annular zone plate, that is, n is 8333, the object distance p is 4.839 mm, and the image distance q is 4.839 mm.

[0106] First, according to the wavelength of extreme ultraviolet light 12.4nm, determine the value of p+q and the value of 750nλ and The value of λ is the same as the value of 50nλ.

[0107] According to the calculation, the value of p+q is 9.678, which is less than the value of 750nλ, 77.5;

[0108] According to calculation, we can get The value of is about 2.407, which is smaller than the value of 50nλ, 5.166.

[0109]

[0110] Therefore, the zone plate structure is designed using formula (1). The zone plate has a diameter of about 1 mm and an outermost ring width of about 30 nm. The numerical simulation is performed and the result obtained as design 1 is as follows: Figure 4 As shown in (a).

[0111] Comparative Example 1

[0112] The same data as in Example 1 are used to calculate the diffraction efficiency of focusing a 100 eV EUV spot 4.839 mm away to 4.839 mm using an 8333 zone plate, i.e., n is 8333, the object distance p is 4.839 mm, and the image distance q is 4.839 mm.

[0113]

[0114] The zone plate is designed using formula (2). The zone plate has a diameter of about 1 mm and an outermost ring width of about 30 nm. The numerical simulation is performed and the result obtained as design 2 is as follows: Figure 4 (b) shown.

[0115] Comparative Example 2

[0116] The same data as in Example 1 are used to calculate the diffraction efficiency of focusing a 100 eV EUV spot 4.839 mm away to 4.839 mm using an 8333 zone plate, i.e., n is 8333, the object distance p is 4.839 mm, and the image distance q is 4.839 mm.

[0117]

[0118] The zone plate is designed using formula (3). The zone plate has a diameter of about 1 mm and an outermost ring width of about 30 nm. The numerical simulation is performed and the result obtained as design 3 is as follows: Figure 4 (c) shown.

[0119] According to Example 1 and Comparative Examples 1-2, as well as the three design methods of the three formulas, the zone plates are modeled and then simulated respectively. The simulation results are obtained by numerical calculation, and the diffraction efficiency of the zone plates designed based on the three schemes is compared. The results are as follows: Figure 4 and Figure 5 shown.

[0120] Figure 4 Comparison diagram of focusing a 100eV extreme ultraviolet light spot 4.839mm away to a spot 4.839mm according to an embodiment of the present invention; (a) is the design method of embodiment 1; (b) is the design method of comparative example 1; (c) is the design method of comparative example 2.

[0121] Figure 5 This is a comparison chart of diffraction efficiency when focusing a 100eV extreme ultraviolet light spot 4.839mm away to 4.839mm according to an embodiment of the present invention.

[0122] according to Figure 4 and Figure 5 It can be seen that although the profiles of the point spread functions are similar, the diffraction efficiency of the zone plate involved in the use of formula (3) in comparative example 2 is lower, and the diffraction efficiency of the zone plate designed using formula (1) in embodiment 1 is 1.5 times that of comparative example 2; the diffraction efficiency of the zone plate designed using formula (2) in comparative example 1 is even lower, and the diffraction efficiency of the zone plate designed using formula (1) in embodiment 1 is thousands of times that of comparative example 1.

[0123] Example 2 Calculation of the diffraction efficiency of the extreme ultraviolet zone plate

[0124] The design method of the present invention is used to calculate the diffraction efficiency of focusing a 100 eV extreme ultraviolet light spot 2419 mm away to 2.422 mm with an 8333 annular zone plate, that is, n is 8333, the object distance p is 2419 mm, and the image distance q is 2.422 mm.

[0125] First, according to the wavelength of extreme ultraviolet light 12.4nm, determine the value of p+q and the value of 750nλ and The value of λ is the same as the value of 50nλ.

[0126] According to the calculation, the value of p+q is 2421.772, which is greater than the value of 750nλ, 77.5;

[0127] According to calculation, we can get The value of 2.419 is smaller than the value of 50nλ, which is 5.166.

[0128]

[0129] Therefore, the zone plate structure is designed using formula (1). The zone plate has a diameter of about 1 mm and an outermost ring width of about 30 nm. The numerical simulation is performed and the result obtained as design 1 is as follows: Figure 6 As shown in (a).

[0130] Comparative Example 3

[0131] The same data as in Example 2 are used to calculate the diffraction efficiency of focusing a 100 eV EUV light spot 2419 mm away to 2.422 mm using an 8333 zone plate, i.e., n is 8333, the object distance p is 2419 mm, and the image distance q is 2.422 mm.

[0132]

[0133] The zone plate is designed using formula (2). The zone plate has a diameter of about 1 mm and an outermost ring width of about 30 nm. The numerical simulation is performed and the result obtained as design 2 is as follows: Figure 6 (b) shown.

[0134] Comparative Example 4

[0135] The same data as in Example 2 are used to calculate the diffraction efficiency of focusing a 100 eV EUV light spot 2419 mm away to 2.422 mm using an 8333 zone plate, i.e., n is 8333, the object distance p is 2419 mm, and the image distance q is 2.422 mm.

[0136]

[0137] The zone plate is designed using formula (3). The zone plate has a diameter of about 1 mm and an outermost ring width of about 30 nm. The numerical simulation is performed and the result obtained as design 3 is as follows: Figure 6 (c) shown.

[0138] According to Example 2 and Comparative Examples 3-4, as well as the three design methods of the three formulas, the wave plate models were established, and then simulations were performed respectively. The simulation results were obtained by numerical calculation, and the diffraction efficiency of the wave zone plates designed based on the three schemes was compared. The results are as follows: Figure 6 and Figure 7 shown.

[0139] Figure 6 Comparison diagram of focusing a 100 eV extreme ultraviolet light spot 2419 mm away to a spot of 2.422 mm according to an embodiment of the present invention; (a) is the design method of embodiment 2; (b) is the design method of comparative example 3; and (c) is the design method of comparative example 4.

[0140] Figure 7 This is a comparison chart of diffraction efficiency when focusing a 100eV extreme ultraviolet light spot 2419mm away to 2.422mm according to an embodiment of the present invention.

[0141] according to Figure 6 and Figure 7 It can be seen that although the profiles of the point spread functions are similar, the diffraction efficiency of the zone plate involved in the use of formula (3) in comparative example 4 is very low, and the diffraction efficiency of the zone plate designed using formula (1) in embodiment 1 is 22.3 times that of comparative example 4; the diffraction efficiency of the zone plate designed using formula (2) in comparative example 3 is basically the same as the diffraction efficiency of the zone plate designed using formula (1) in embodiment 1.

[0142] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are 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 in the scope of protection of the present invention.

Claims

1. A method for designing an extreme ultraviolet zone plate, wherein: include: Determine a preset object distance p; Determine the preset image distance q; Determine the extreme ultraviolet wavelength λ; When the value of p+q is less than 750nλ, the radius of the nth ring zone r is obtained according to formula (1): n : At values ​​of p+q greater than or equal to 750nλ and When the value of is less than 50nλ, the radius of the nth ring zone r is obtained according to formula (2): n : At values ​​of p+q greater than or equal to 750nλ and When the value of is greater than or equal to 50nλ, the radius of the nth ring zone r is obtained according to formula (3): n : According to r n The radius of each zone of the EUV zone plate is designed based on the value; The extreme ultraviolet zone plate is designed according to the preset diameter and outermost ring width of the extreme ultraviolet zone plate, as well as the radii of each ring zone.

2. A method for preparing an extreme ultraviolet zone plate, comprising: Determining a photolithographic layout of an EUV zone plate according to the design method of claim 1; Spin coating hydrogen silsesquioxane photoresist on a silicon nitride window, wherein the silicon nitride window has a silicon wafer as a supporting substrate; exposing the silicon nitride window spin-coated with hydrogen silsesquioxane photoresist using an electron beam lithography machine according to the photolithography pattern, wherein the hydrogen silsesquioxane photoresist forms amorphous silicon dioxide under electron beam irradiation; placing the exposed silicon nitride window in a developer for development; The developed silicon nitride window is dried to obtain an extreme ultraviolet zone plate.

3. The preparation method according to claim 2, wherein Placing the exposed silicon nitride window in a developer for development includes: The exposed silicon nitride window is placed in 25% by mass tetramethylammonium hydroxide for development for 55 to 65 seconds, and fixed in water for 25 to 35 seconds; The fixed silicon nitride window was placed in isopropyl alcohol and allowed to stand for 4 to 6 minutes.

4. The preparation method according to claim 3, wherein The film is placed in 25% by mass of tetramethylammonium hydroxide for development for 60 seconds and fixed in water for 30 seconds; The mixture was placed in isopropyl alcohol and allowed to stand for 5 minutes.

5. The preparation method according to claim 2, wherein The thickness of the hydrogen silsesquioxane photoresist spin-coated on the silicon nitride window is 60 nm.

6. The preparation method according to claim 2, wherein Also includes: After spin coating hydrogen silsesquioxane photoresist on the silicon nitride window, pre-bake in an environment of 80 to 100° C. for 3 to 8 minutes.

7. The preparation method according to claim 2, wherein Drying the developed silicon nitride window includes: The developed silicon nitride window was blown dry by an air gun.

8. An extreme ultraviolet zone plate prepared by the preparation method according to any one of claims 2 to 7.

9. Use of the extreme ultraviolet zone plate according to claim 8 in synchrotron radiation probe technology. 10 . The use according to claim 9 , wherein the EUV zone plate is used to focus light in the EUV band into a light spot smaller than 100 nm.

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