A method for designing a wide-spectrum extreme ultraviolet focusing optical path system

Abstract

The application discloses a kind of wide spectrum extreme ultraviolet focusing optical path system design methods.Cascaded cylindrical mirror group focusing optical path system is proposed, which can compensate for aberration under the configuration of high focusing ability on the basis of reducing processing cost, thereby obtaining the effect of high imaging quality;It solves the problem that the processing cost, imaging quality and focusing ability are difficult to balance in the traditional grazing incidence reflection focusing optical path system.The design proposed by the application has good practical application significance in the field of extreme ultraviolet research, especially in the field of industrial application.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and in particular to a design method for a broadband extreme ultraviolet focusing optical path system. Background Technology

[0002] Extreme ultraviolet (EUV) light refers to electromagnetic radiation with a vacuum wavelength between approximately 5 nm and 40 nm. Unlike other wavelengths, the EUV to soft X-ray band contains a large amount of atomic resonance line radiation, which is easily absorbed by various substances (including air). Therefore, EUV and soft X-ray applications require a high-vacuum environment. This characteristic poses challenges to EUV light sources and optical systems, and also imposes vacuum compatibility requirements on other hardware structures, including electronic circuits. EUV applications mainly include EUV lithography, EUV spectrometers, and solar EUV space telescopes.

[0003] From the perspective of light source, extreme ultraviolet (EUV) sources can be categorized into synchrotron sources and non-synchrotron sources based on their size. Synchrotron sources represent a country or region's research capabilities in related fields; the light sources they provide represent the most advanced levels achievable today in terms of coherence, singleness of light source, and light intensity. Therefore, synchrotrons often house large research teams conducting research on the applications of EUV, soft X-rays, and hard X-rays. However, for industry, the enormous construction and maintenance costs of synchrotrons, with their hundreds or even thousands of meters of optical path length, are impractical. Furthermore, offline asynchronous processing or measurement of workpieces within synchrotrons becomes a key obstacle to achieving mass production. The demand in industrial applications lies in using relatively small-sized EUV equipment that meets processing and measurement requirements, including EUV light sources and optical systems, to integrate with other production equipment for mass production. Non-synchrotron accelerator light sources mainly refer to extreme ultraviolet light sources based on discharge plasma (DPP) and laser plasma (LPP). Their size is often compatible with laboratory settings, and can even reach desktop size, thus becoming a demand for industrial applications.

[0004] Extreme ultraviolet (EUV) light shares similar optical properties with X-rays, with a refractive index less than or approximately 1 in any material and being readily absorbed by various substances. Therefore, the related optical focusing systems must differ from conventional optical systems. In principle, focusing optical systems for EUV and X-rays can be categorized into three types: refraction, diffraction, and reflection. Extreme ultraviolet (EUV) and X-rays have refractive indices very close to 1, meaning that single-refractive methods cannot produce sufficient focusing power, often requiring focal lengths of tens of meters or more. This changed in the 1990s when Tomie proposed compound refractive lenses, using stacked ultrathin lenses to achieve shorter focal lengths. Diffraction-based optical systems, such as Fresnel zone plates, can focus monochromatic wavelengths. For reflection-based optical systems, multi-layered coated lenses can operate under near-direct incidence conditions, focusing monochromatic wavelengths and achieving large numerical apertures and low aberrations. Single-layered coated mirrors generally operate under grazing incidence conditions, requiring the grazing incidence angle to be less than the critical angle for total external reflection. For X-rays, the critical angle is often less than 1°, while for EUV, this critical angle can reach over 10°. As shown in the figure, the wavelength of the radiation must be considered in all optical system applications. For compound refractive lenses, Fresnel zone plates, and multilayer coated mirrors, different wavelengths of radiation lead to different focal lengths or different optical structures in the system. However, for grazing-incidence mirrors, once the total external reflection condition is met for radiation across all wavelengths, their effect on light does not change with wavelength. Therefore, for broadband extreme ultraviolet applications, grazing-incidence mirrors are the only choice.

[0005] Grazing-incidence mirrors for extreme ultraviolet or X-ray applications mainly come in two forms: Kirkpatrick-Baez mirrors and Wolter mirrors. Based on their focusing capabilities, they can be categorized as one-dimensional or two-dimensional focusing mirrors. The mirror surface shape is generally obtained by translating or rotating a quadratic curve. Quadratic curve translation yields one-dimensional cylindrical mirrors, such as cylinders, elliptical cylinders, parabolic cylinders, and hyperboloid cylinders. Rotation of a quadratic curve yields spherical, toroidal, ellipsoidal, parabolic, and hyperboloid surfaces. In terms of manufacturing difficulty and cost, two-dimensional focusing mirrors are more difficult and expensive to manufacture than one-dimensional focusing mirrors, and aspherical focusing mirrors are more difficult and expensive to manufacture than spherical (cylindrical) focusing mirrors. Kirkpatrick and Baez verified that X-ray focusing can be achieved using orthogonal cylindrical mirror assemblies; however, the numerical aperture of the overall optical system is too small, and there are significant aberrations and poor resolution. Wolter-type mirrors can improve image quality, but their manufacturing cost is extremely high, and they are generally only used in space telescope projects. Because the wavelength of EUV / X-rays is more than two orders of magnitude smaller than that of conventional visible light, the requirements for the manufacturing error of the focusing mirror surface are also increased by an order of magnitude.

[0006] Therefore, in current extreme ultraviolet focusing optical path systems, the use of grazing incidence mirrors often encounters two situations. If low-cost cylindrical or spherical mirrors are used, their imaging quality and focusing ability conflict. That is, the greater the focusing ability (the greater the magnification of the optical system), the greater the optical aberration, thus reducing the imaging quality. Only when the object point and image point are located on the Rowland circle can a near-zero aberration imaging effect be achieved. If high imaging quality and high focusing ability are to be achieved simultaneously, then more expensive aspherical focusing mirrors are often required, such as elliptical cylinders, parabolic cylinders, hyperboloid cylinders, as well as ellipsoidal, parabolic, and hyperboloid mirrors, collectively known as "Cartesian" surface mirrors.

[0007] Therefore, how to achieve a low processing cost, high imaging quality, and large focusing capability in an extreme ultraviolet grazing incidence reflective focusing optical path system is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] To address the problems in the background art, this invention proposes a design method for a broadband extreme ultraviolet focusing optical path system.

[0009] The technical solution adopted in this invention is as follows:

[0010] I. A broadband extreme ultraviolet focusing optical path system

[0011] It includes cascaded cylindrical focusing mirrors, at least one of which is a concave lens; the cascaded cylindrical focusing mirrors are arranged in a Z-shape or a U-shape; and broadband extreme ultraviolet light is focused by the cascaded cylindrical focusing mirrors.

[0012] II. A Design Method for a Broadband Extreme Ultraviolet Focusing Optical Path System

[0013] Includes the following steps:

[0014] Step 1) Obtain the range of grazing incidence angles under specific emissivity requirements;

[0015] Step 2) Based on the diffraction limit, perform aperture verification of the optical path system to obtain the shortest length required for the mirror;

[0016] Step 3) Compensate for coma by using cascaded cylindrical mirrors, thereby improving the image quality at the focal point;

[0017] Step 4) Based on the aberration compensation conditions in Step 3), design aberration compensation conditions for cascaded cylindrical mirrors with different arrangements.

[0018] The specific emissivity in step 1) is the design parameter requirement that the overall system imposes on individual optical modules.

[0019] In step 1), based on the broadband band of the focused extreme ultraviolet light and the material selected for the film layer on the surface of the reflector, the reflectivity of the extreme ultraviolet light incident on the surface of the reflector at different incident angles is calculated and simulated, thereby obtaining the maximum grazing incident angle under a specific reflectivity requirement.

[0020] Step 2) specifically refers to:

[0021] The full width at half maximum (FWHM) of the Airy disk in an optical system diffraction for:

[0022]

[0023] In the formula, λ is the extreme ultraviolet wavelength, NA is the numerical aperture of the mirror on the image side, L is the mirror length, θ is the grazing incidence angle, and Arm exit The length of the launching arm;

[0024] Based on the requirements for Airy disk size, exit arm length, and grazing incidence angle, the above formula is transformed to obtain the shortest length required for the reflector:

[0025] L>1.76·λ·Arm exit / (r diffraction *sinθ).

[0026] When the output arm length is selected as 100mm, the wavelength as 20nm, and the grazing incidence angle as 15°, rdiffraction If the value is 1μm, then the length of the reflector needs to be greater than 13.6mm.

[0027] The size of the Airy spot must be smaller than the minimum spot size required by the design.

[0028] When designing an optical system, it is necessary to ensure that the optical system can provide a sufficient numerical aperture to result in a small diffraction limit and avoid the size of the diffraction Airy disk exceeding the minimum resolution requirement of the system; that is, the optical design should first ensure that the size of the diffraction Airy disk is smaller than the minimum spot size required by the design.

[0029] Step 3) specifically refers to:

[0030] The main aberration of a single cylindrical mirror is coma. The coma produced at the positive focal position and the negative focal position is in opposite directions. Therefore, coma can be compensated by using two cylindrical mirrors to produce coma of opposite directions and the same magnitude at the positive focal position and the negative focal position, respectively. This reduces the spot size of the focused broadband extreme ultraviolet light.

[0031] 3.1) Convert the transverse aberration of coma into the form of axial aberration:

[0032]

[0033] In the formula, △ represents axial coma, and T coma For transverse coma, The angle at which the light ray at the intermediate focal plane deviates from the principal ray; The angle of incidence is M, where M represents the magnification of the optical system and q is the length of the exit arm.

[0034] 3.2) The aberration compensation strategy between cascaded cylindrical mirrors is as follows: when two mirrors emit beams of the same angle at the central focal plane, the resulting axial aberrations are equal in magnitude and mutually compensate for each other.

[0035] That is when hour,

[0036] In the formula, and These represent the angles by which the light rays from the first and second cylindrical mirrors deviate from the principal ray at the central focal plane, respectively. and These represent the axial coma of the first and second cylindrical mirrors, respectively.

[0037] In step 3.1), the magnification of the optical system is M = q / p, where q is the length of the exit arm and p is the length of the incident arm.

[0038] In step 4):

[0039] For a cascaded cylindrical mirror arranged in a U-shape, the relationship between the two exit angles satisfies the aberration compensation formula as follows: From the aberration compensation condition formula, we can obtain:

[0040]

[0041] In the formula, θ1 and θ2 are the grazing incident angles of the first and second cylindrical mirrors (the first cylindrical mirror is closer to the light source), M1 and M2 are the magnifications of the first and second cylindrical mirrors, q1 is the exit arm length of the first cylindrical mirror, and q2 is the incident arm length of the second cylindrical mirror.

[0042] Simplifying, we get:

[0043]

[0044] For cascaded cylindrical mirrors arranged in a Z-shape, the relationship between the two exit angles satisfies the aberration compensation formula as follows: From the aberration compensation condition formula, we can obtain:

[0045]

[0046] Simplifying, we get:

[0047]

[0048] Therefore, the conditions for aberration compensation can be described mathematically as follows:

[0049]

[0050] Design a focusing optical path system based on aberration compensation conditions and the following conditions:

[0051] a) M1*M2=r spot / R

[0052] In the formula, r spot R represents the size of the focused light spot that the focusing optical path system needs to achieve; R is the size of the object-side light source of the focusing optical path system.

[0053] b) By adjusting the length p2 of the exit arm of the second cylindrical mirror, interference is prevented between the second cylindrical mirror and the mechanical structure at the focal point;

[0054] c) θ1 and θ2 are less than the maximum grazing incidence angle;

[0055] d) Mirror length L > 1.76·λ·Arm exit / (r diffraction *sinθ).

[0056] The beneficial effects of this invention are as follows:

[0057] This invention addresses the challenge of balancing manufacturing cost, image quality, and focusing capability in traditional grazing incidence reflection focusing optical path systems. It proposes a cascaded cylindrical mirror group focusing optical path system that, while reducing manufacturing costs, compensates for aberrations with high focusing capability, thereby achieving high image quality. The design proposed in this invention has significant practical application value in the field of extreme ultraviolet research, particularly in industrial applications. Attached Figure Description

[0058] Figure 1 It is the curve showing the relationship between the reflectivity of a grazing incidence mirror and the incident angle;

[0059] Figure 2 The difference in image quality is due to the cylindrical reflector.

[0060] Figure 3 It is an aberration compensation strategy for cascaded cylindrical mirrors;

[0061] Figure 4 It consists of cascaded cylindrical mirror groups arranged in a "U" shape and a "Z" shape: (a) concave mirror group; (b) convex and concave mirror group; (c) concave and convex mirror group;

[0062] Figure 5 This is a parameter table for a cascaded cylindrical concave mirror with aberration compensation. Detailed implementation method:

[0063] The following will provide a more detailed description of a camera mounting angle correction method provided by the present invention.

[0064] The present invention will now be described in more detail with reference to the accompanying drawings, which illustrate preferred embodiments of the invention. It should be understood that those skilled in the art can modify the invention described herein while still achieving its advantageous effects. Therefore, the following description should be understood as being of general knowledge to those skilled in the art and is not intended to limit the invention.

[0065] For clarity, not all features of the actual embodiments are described. In the following description, well-known functions and structures are not detailed in detail, as they would obscure the invention with unnecessary detail. It should be understood that in the development of any actual embodiment, numerous implementation details must be made to achieve the developer's specific objectives, such as changes from one embodiment to another according to limitations related to the system or business. Furthermore, it should be understood that such development work may be complex and time-consuming, but is merely routine work for those skilled in the art.

[0066] To make the objectives and features of the present invention more apparent and understandable, the specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that the drawings are all in a very simplified form and use non-precise ratios, and are only used to conveniently and clearly assist in illustrating the objectives of the embodiments of the present invention. Specific implementation examples:

[0068] A design method for a broadband extreme ultraviolet focusing optical path system, the specific design steps of which are as follows:

[0069] Step 1) Grazing incidence angle verification

[0070] Based on the broadband wavelength of the focused extreme ultraviolet light and the material selected for the film layer on the reflector surface, the reflectivity under different incident angles is calculated and simulated, thus obtaining the grazing incident angle requirement corresponding to a specific reflectivity requirement. Figure 1 The figure shows the reflectivity analysis of a ruthenium-coated mirror for broadband extreme ultraviolet light (10-20nm) and under grazing incidence angles of 0-20°. As can be seen from the figure, in order to ensure that the reflectivity of extreme ultraviolet light in all bands can reach more than 55%, the grazing incidence angle needs to be less than 15°.

[0071] Step 2) Aperture verification of optical path system

[0072] When designing an optical system, it is necessary to ensure that the system provides a sufficient numerical aperture to achieve a small diffraction limit and prevent the size of the diffraction Airy disk from exceeding the minimum resolution requirement of the system. In other words, the optical design must first ensure that the size of the diffraction Airy disk is smaller than the minimum required spot size. The full width at half maximum (FWHM) of the Airy disk in the optical system is:

[0073]

[0074] In the formula, λ is the extreme ultraviolet wavelength, NA is the numerical aperture of the mirror on the image side, L is the mirror length, θ is the grazing incidence angle, and Arm exit Given the length of the exit arm, and based on the requirements of the Airy disk size, exit arm length, and grazing incidence angle, the minimum length required for the reflector can be calculated, thus limiting the length requirement of the reflector, as shown in the following formula:

[0075] L>1.76·λ·Arm exit / (r diffraction *sinθ)

[0076] If the length of the output arm is selected as 100mm, the wavelength is selected as 20nm, and the grazing incidence angle is 15°, then the length of the reflector needs to be greater than 13.6mm.

[0077] Step 3) Aberration Analysis

[0078] For monolithic cylindrical / spherical / ring-shaped mirrors, a typical application is to use single-magnification optical capabilities, with both the object and image points located on the Rowland circle, resulting in aberration-free imaging. This setup is frequently used in cylindrical diffraction gratings, achieving spectral separation while maximizing spatial resolution. However, when the required magnification deviates significantly from unity magnification, the drastically increased aberrations introduced by using a monolithic cylindrical mirror must be taken into account.

[0079] Aberrations can be analyzed using wave aberration. According to Fermat's principle, when the optical path length from the object point to the image point via any point on the aperture is constant, it indicates that aberration-free imaging quality is achieved, which is the imaging relationship between the two conjugate focal points in a Cartesian surface mirror. Conversely, any optical path difference within the aperture range represents the existence of aberrations. Therefore, the derivation of aberrations can begin with the calculation of optical path length.

[0080] like Figure 2 As shown, light rays originate from point source P, are reflected by the surface of the mirror, and reach image point Q. The incident arm length is PO = p, the grazing incidence angle is θ, and the exit arm length is OQ = q. The optical path length through any point O' on the mirror surface can be defined as F = PO' + O'Q, and this value can be represented by parameters p, q, θ, R, and y, where R is the radius of curvature of the mirror, and y represents the lateral coordinate of the mirror surface.

[0081] F=PO'+O'Q=p+q+F2+F3+F4+O(y 5 )

[0082] The optical path length coinciding with the principal optical axis is POQ = p + q. Therefore, the optical path difference between the optical path length F and this value represents the aberration, which is the remaining term after removing the incident and exit arm lengths in the formula. These optical path differences can be rearranged according to the order of the mirror coordinate value y. Aberrations of the fifth order and above are omitted here. Subsequent analysis will also show that aberrations mainly exist in low-order coma. Here, expanding the second, third, and fourth order terms of the coordinate value y respectively yields:

[0083]

[0084]

[0085]

[0086] Here, F2 represents the aberration caused by defocusing, from which the condition required for focused imaging can be derived; F3 represents coma, and F4 represents spherical aberration. When the mirror operates according to the Rowland configuration, p = q = Rcosα, and it can be seen that coma is completely eliminated, and most of the spherical aberration is also eliminated. However, when a cylindrical mirror is required to produce a large focusing capability, i.e., a small magnification, these aberrations become non-negligible. Generally speaking, the optical system will satisfy its focusing condition, i.e., F2 = 0, which can be obtained as follows:

[0087]

[0088] The transverse aberration is defined as the distance between the image point formed by any ray in the image plane and the image point formed by the principal ray. The magnitude of the transverse aberration, T, can be obtained by differentiating the optical path difference.

[0089]

[0090] Substituting the focusing conditions mentioned earlier, we can obtain the transverse aberration expressions for coma and spherical aberration:

[0091]

[0092]

[0093] In the formula, M refers to the magnification of the optical system, M = q / p. When focusing capability exists, spherical aberration is often much smaller than coma. If it is required that all aberration rays caused by coma fall on a specific size r... spot Within the light spot area, i.e., T coma <r spot The requirements for the aperture size of the reflecting mirror are as follows:

[0094]

[0095] Numerical analysis reveals the constraints on the aperture size of the reflector. Only when M is close to 1, i.e., when the reflector approaches unity magnification, can the constraints on the reflector length in step 2) be simultaneously satisfied. In other words, for a single cylindrical reflector, due to its inherent large aberrations, this optical system cannot simultaneously meet the requirements for both aberrations and diffraction spot size. For example, when the required spot size is r... spot =1μm, and given the operating conditions of the cylindrical mirror as a magnification of 0.1x, an exit arm length of 100mm, and a grazing incidence angle of 10°, the required mirror size y < 0.89mm can be calculated. At this point, the spherical aberration is T. spherical =

[0096] At 0.0125 μm, we can see that spherical aberration and coma differ by nearly two orders of magnitude. Therefore, it is reasonable to consider coma as the main aberration in a cylindrical mirror, and subsequent aberration analysis can focus primarily on coma. Meanwhile, the condition that the mirror size y < 0.89 mm cannot be simultaneously satisfied with the mirror length requirement in step 2).

[0097] Step 4) Aberration Compensation

[0098] Aberration analysis of a single cylindrical mirror reveals that coma is the primary aberration in its imaging. Therefore, coma can be compensated by cascading cylindrical mirrors, thereby improving image quality at the focal point. The aberration compensation strategy between cylindrical mirrors is as follows: Observing the two cylindrical mirrors from both the object and image points, when they emit beams of light at the same angle at the central focal plane, the resulting axial aberrations are equal in magnitude and mutually compensating. Axial aberration is used here instead of transverse aberration because, for the main component of aberration, coma, its transverse aberration is always distributed on one side of the optical axis, thus making it impossible to distinguish the beams on either side of the principal ray based on the value of the transverse aberration. Therefore, before analyzing aberration compensation, the previously obtained transverse aberration needs to be converted into axial aberration form. The value of axial coma can be obtained from the expression for transverse coma:

[0099]

[0100] The aberration compensation method described above can be expressed mathematically as follows: hour,

[0101]

[0102] Step 5) Topology Analysis

[0103] The aberration compensation conditions in step 4) regarding the relationship between φ1 and φ2 and the sign of the entrance and exit arm lengths need to be discussed based on the relative positions of the mirrors and the sign of their curvature. For cascaded cylindrical focusing mirrors, the signs of the curvature of the two mirrors can be selected from concave and convex surfaces. However, to ensure the focusing capability of the optical system, at least one mirror needs to be a concave lens. Furthermore, the mirrors can be arranged in a "Z" or "U" shape, resulting in a total of six possible topologies for cascaded cylindrical mirrors.

[0104] For a pair of mirrors arranged in a "U" shape, the relationship between the two exit angles satisfies the aberration compensation formula as follows: From the aberration compensation condition formula, we can obtain...

[0105]

[0106] Simplifying, we get

[0107]

[0108] Similarly, for a cascaded cylindrical mirror arranged in a "Z" shape, the conditions that need to be met to achieve aberration compensation are as follows:

[0109]

[0110] Therefore, the conditions for aberration compensation can be described mathematically as follows:

[0111]

[0112] Figure 5 The diagram shows a cascaded cylindrical concave mirror with aberration compensation. The parameters in the table further illustrate the specific functions of the two mirrors: the first mirror provides a larger optical focusing effect, but this comes with a short exit arm length and significant aberrations; the second mirror primarily provides the exit arm length required by the design and compensates for the aberrations. Furthermore, the aberration compensation conditions proposed in this invention, in practical optical design, can be achieved by using two cylindrical mirrors with the same radius of curvature, installed with different entrance and exit arm lengths and grazing incidence angles, to achieve aberration compensation. This approach can further reduce the custom manufacturing cost of the mirrors.

Claims

1. A design method for a broadband extreme ultraviolet (EUV) focusing optical path system, the method employing a broadband EUV focusing optical path system, the system comprising cascaded cylindrical focusing mirrors, wherein at least one mirror is a concave lens; the cascaded cylindrical focusing mirrors are arranged in a Z-shape or a U-shape; and broadband EUV light is focused by the cascaded cylindrical focusing mirrors. Its features are, Includes the following steps: Step 1) Obtain the range of grazing incidence angles under specific emissivity requirements; Step 2) Based on the diffraction limit, perform aperture verification of the optical path system to obtain the shortest length required for the mirror; Step 3) Compensate for coma by using cascaded cylindrical mirrors, thereby improving the image quality at the focal point; Step 4) Based on the aberration compensation conditions in Step 3), design aberration compensation conditions for cascaded cylindrical mirrors with different arrangements. Step 3) specifically refers to: The main aberration of a single cylindrical mirror is coma. The coma produced at the positive focal position and the negative focal position is in opposite directions. Therefore, coma can be compensated by using two cylindrical mirrors to produce coma of opposite directions and the same magnitude at the positive focal position and the negative focal position, respectively. This reduces the spot size of the focused broadband extreme ultraviolet light. 3.1) Convert the transverse aberration of coma into the form of axial aberration: In the formula, Indicates axial coma. For transverse coma, θ is the angle at which the ray at the intermediate focal plane deviates from the principal ray; θ is the grazing incidence angle; M represents the magnification of the optical system; and q is the length of the exit arm. 3.2) The aberration compensation strategy between cascaded cylindrical mirrors is as follows: when two mirrors emit beams of the same angle at the central focal plane, the resulting axial aberrations are equal in magnitude and mutually compensate for each other. That is when hour, ; In the formula, and These represent the angles by which the light rays from the first and second cylindrical mirrors deviate from the principal ray at the central focal plane, respectively. and These represent the axial coma of the first and second cylindrical mirrors, respectively. In step 4): 4.1) For a U-shaped arrangement of cascaded cylindrical mirrors, the relationship between the two exit angles satisfies the aberration compensation formula as follows: From the aberration compensation condition formula in step 3), we can obtain: In the formula, and These are the grazing incidence angles of the first and second cylindrical mirrors, respectively. and These represent the magnification of the first and second cylindrical mirrors, respectively. The length of the exit arm of the first cylindrical mirror. This is the length of the incident arm of the second cylindrical mirror; Simplifying, we get: 4.2) For a cascaded cylindrical mirror arranged in a Z-shape, the relationship between the two exit angles satisfies the aberration compensation formula as follows: From the aberration compensation condition formula, we can obtain: Simplifying, we get: Therefore, the final expression for the aberration compensation condition is: 。 2. The design method of a broadband extreme ultraviolet focusing optical path system according to claim 1, characterized in that, In step 1), based on the broadband band of the focused extreme ultraviolet light and the material selected for the film layer on the surface of the mirror, the reflectivity of the extreme ultraviolet light incident on the surface of the mirror at different incident angles is calculated and simulated, so as to obtain the maximum grazing incident angle under a specific reflectivity requirement.

3. The design method of a broadband extreme ultraviolet focusing optical path system according to claim 1, characterized in that, Step 2) specifically refers to: Full width at half maximum (FWHM) of Airy disk in an optical system for: In the formula, Where λ is the extreme ultraviolet wavelength, NA is the numerical aperture of the mirror on the image side, and L is the length of the mirror. For the grazing incidence angle, The length of the launching arm; Based on the requirements for Airy disk size, exit arm length, and grazing incidence angle, the above formula is transformed to obtain the shortest length required for the reflector: 。 4. The design method of a broadband extreme ultraviolet focusing optical path system according to claim 3, characterized in that, The size of the Airy spot must be smaller than the minimum spot size required by the design.

5. The design method of a broadband extreme ultraviolet focusing optical path system according to claim 1, characterized in that, In step 3.1), the magnification of the optical system q is the length of the launch arm. The incident arm length.

6. The design method of a broadband extreme ultraviolet focusing optical path system according to claim 1, characterized in that, Design a focusing optical path system based on aberration compensation conditions and the following conditions: a)M1*M2= / R In the formula, R represents the size of the focused light spot that the focusing optical path system needs to achieve; R is the size of the object-side light source of the focusing optical path system. b) Adjust the length of the exit arm of the second cylindrical mirror. To prevent interference between the second cylindrical mirror and the mechanical structure at the focal point; c) and Less than the maximum grazing incidence angle.

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