Extreme ultraviolet high-resolution monochromation method and system

Abstract

This invention discloses an extreme ultraviolet (EUV) high-resolution monochromaticization method and system, relating to the field of spectral technology. The EUV high-resolution monochromaticization method includes: S1, providing an incident light source; S2, setting an off-axis parabolic mirror as a collecting mirror, which receives the EUV light beam and collimates it into parallel light; S3, setting a grating to split the parallel light, the parallel light is incident on the grating at a preset angle along the grating's etched lines, forming conical diffraction. Rotating the grating adjusts the incident azimuth angle α of the parallel light, causing EUV light of different wavelengths to propagate along different diffraction azimuth angles β. This EUV high-resolution monochromaticization method, through the use of two off-axis parabolic mirrors, fundamentally avoids chromatic aberration and spherical aberration, ensuring high reflection efficiency in the EUV band. The use of conical diffraction results in high diffraction efficiency, uniform distribution of the light spot in the confocal plane, and ease of spot selection, thereby reducing linear dispersion and increasing resolution.

Description

Technical Field

[0001] This invention relates to the field of spectroscopy, and more specifically, to an extreme ultraviolet high-resolution monochromaticization method and system. Background Technology

[0002] Extreme ultraviolet (EUV) monochromatic technology is one of the core supporting technologies in fields such as spectroscopy, materials science, and photolithography. Its performance directly affects spectral resolution, energy utilization, and the accuracy of experimental data.

[0003] Traditional extreme ultraviolet (EUV) monochromators typically employ a combination of a spherical mirror and a conventional in-plane diffraction grating. In this traditional structure, the inherent spherical and chromatic aberrations of the spherical mirror lead to insufficient focusing accuracy of the dispersed beam, severely impacting resolution. Even with pre-collimation of the converging beam from the light source, the parallel light after conventional collimation still exhibits inherent aberrations, failing to guarantee uniform light intensity and only meeting the basic requirement of parallel light incidence, making fine dispersion of EUV light difficult. Furthermore, under low grazing angle conditions in the EUV band, conventional in-plane diffraction gratings exhibit significant shadowing effects, resulting in severe photon loss and generally low diffraction efficiency. Therefore, with insufficient resolution and low diffraction efficiency, achieving high-fidelity, high-resolution monochromatic output of EUV light is challenging. Summary of the Invention

[0004] This invention provides a method and system for high-resolution monochromatic extreme ultraviolet light, which can solve the problem that the low diffraction efficiency and insufficient resolution in the prior art make it difficult to achieve high-fidelity, high-resolution monochromatic output of extreme ultraviolet light.

[0005] A high-resolution extreme ultraviolet monochromatic method includes the following steps: S1. Provides an incident light source that emits Gaussian extreme ultraviolet laser with a divergence angle; S2. An off-axis parabolic reflector is set as a collecting mirror, which receives the extreme ultraviolet light beam and collimates it into parallel light. S3. A grating is set up to split parallel light. The grating is a reflective plane grating. The parallel light collimated by the collecting mirror is incident on the grating at a preset angle along the grating etched line direction to form conical diffraction. The grating is rotated to adjust the incident azimuth angle α of the parallel light so that extreme ultraviolet light of different wavelengths propagates along different diffraction azimuth angles β. S4. Set an off-axis parabolic reflector as a focusing mirror and adjust the distance between the focusing mirror (3) and the grating (2) to adjust the linear dispersion. A slit is provided on one side of the focusing mirror. The focusing mirror receives the monochromatic parallel light after the grating is diffracted by a cone and focuses it to the slit so that the monochromatic parallel light forms monochromatic light and the monochromatic light is emitted from the slit. S5. Select monochromatic light of the target wavelength through the slit.

[0006] The extreme ultraviolet high-resolution monochromatic method provided by this invention has, but is not limited to, the following beneficial effects compared to existing technologies: This high-resolution extreme ultraviolet monochromatic method employs an integrated process of collimation by a collecting mirror, grating conical diffraction for beam splitting, focusing by a focusing mirror, and slit selection. Combined with the use of dual off-axis parabolic mirrors, it fundamentally avoids chromatic aberration and spherical aberration, ensuring high reflection efficiency in the extreme ultraviolet band. Unlike conventional perpendicular-incidence diffraction, the conical diffraction method allows for spot selection of extreme ultraviolet light by simply adjusting the slit position and the grating's tilt angle. This enables the selection of monochromatic light in different wavelengths, resulting in high diffraction efficiency, uniform spot distribution in the confocal plane, and easy spot selection. Furthermore, by adjusting the distance between the focusing mirror and the grating, the beams of different wavelengths can be further separated, reducing linear dispersion and increasing resolution. This results in clearer spatial separation, more concentrated energy, and a more regular distribution of monochromatic light after beam splitting.

[0007] Furthermore, in S1, the light source is one of a DPP light source, an LPP light source, a single-mode laser, or a spectral correction lamp.

[0008] Furthermore, in S3, conical diffraction satisfies the grating propagation equation: ; in, m is the diffraction order; λ is the wavelength; σ is the grating constant; γ is the angle between the light beam and the plane of the grating lines; α is the incident azimuth angle; β is the diffraction azimuth angle.

[0009] Furthermore, in S3, the diffraction azimuth angle β is controlled by adjusting the incident azimuth angle α, so that the monochromatic light of the target wavelength is incident on the center of the focusing mirror to separate different monochromatic lights.

[0010] The present invention provides an extreme ultraviolet high-resolution monochromatic system, which is applicable to the extreme ultraviolet high-resolution monochromatic method described above. The extreme ultraviolet high-resolution monochromatic system includes: a collecting mirror, a grating, a focusing mirror and a slit arranged sequentially along the optical path of the extreme ultraviolet laser. Both the collecting mirror and the focusing mirror are off-axis parabolic mirrors, and the collecting mirror is used to collimate the diverging extreme ultraviolet laser into parallel light, while the focusing mirror is used to focus the parallel light. The grating is used to split parallel light using conical diffraction.

[0011] Since the technical improvements and beneficial effects of the extreme ultraviolet high-resolution monochromatic system are at least the same as those of the extreme ultraviolet high-resolution monochromatic method, the extreme ultraviolet high-resolution monochromatic system will not be described in detail here.

[0012] Furthermore, the collecting mirror has an incident angle of 84°, a focal length of 300nm, and a gold film coated on its surface.

[0013] Furthermore, the focusing lens has an incident angle of 84°, a focal length of 1000nm, and a gold film coated on its surface.

[0014] Furthermore, the grating is a reflective planar grating with a grating line count of 1200 lines / mm, and the groove direction of the grating is parallel to the optical axis.

[0015] Furthermore, the distance from the focusing lens to the slit is the equivalent exit focal length L. B The linear dispersion of the system is proportional to cosβ and proportional to L. B The diffraction order m is inversely proportional to the line density n; Where β is the diffraction azimuth angle.

[0016] Furthermore, the slit is located at the focal point of the focusing lens to filter target monochromatic light, and the width of the slit is 50 micrometers. Attached Figure Description

[0017] Figure 1 This is a flowchart of an extreme ultraviolet high-resolution monochromatic method according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of an extreme ultraviolet high-resolution monochromatic system according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of an extreme ultraviolet high-resolution monochromatic system in practical applications. Figure 4 A schematic diagram of the optical path for collecting a point source beam using an off-axis parabolic mirror; Figure 5 This is a schematic diagram of grating conical diffraction; Figure 6 The distribution of light spots on the confocal plane after diffraction of monochromatic light at different wavelengths; Figure 7 This is a schematic diagram showing the diffraction wavelength of an extreme ultraviolet high-resolution monochromatic system corresponding to the α angle.

[0018] Explanation of reference numerals in the attached figures: 1. Collecting mirror; 2. Grating; 3. Focusing mirror; 4. Slit. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings showing multiple embodiments according to this application. It should be understood that the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments described in this application without creative effort will fall within the scope of protection of this application.

[0020] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing specific embodiments only and is not intended to limit this application; the terms "comprising," "including," "having," "containing," etc., in the description, claims, and accompanying drawings of this application are open-ended terms. Therefore, "comprising," "including," or "having" refers to, for example, a method or apparatus having one or more steps or elements, but is not limited to having only these one or more elements. The terms "first," "second," etc., in the description, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0021] In the description of this invention, it should be understood that the terms "upper", "lower", "left", "right", "front", "rear", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0023] It should be emphasized that when the term "comprising / including" is used in this specification, it is used to explicitly indicate the presence of the stated feature, integer, step, or component, but does not exclude the presence or addition of one or more other features, integers, steps, parts, or groups of features, integers, steps, or parts.

[0024] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0025] In commonly used monochromatic techniques, the coupling problem between low efficiency caused by shading effects and low resolution caused by aberrations is the most difficult to solve. In traditional solutions, improving one aspect often sacrifices the other. To reduce shading effects, the grating incident angle or groove direction needs to be changed. However, the geometry of traditional in-plane diffraction limits the adjustment space, and forced adjustments will exacerbate aberrations and reduce resolution.

[0026] To correct aberrations, variable line spacing gratings or additional optical elements are required, but this increases system complexity, further reduces energy efficiency, and cannot fundamentally solve the shadowing effect.

[0027] Specifically, visible light sources are bright enough that there's no need to capture more beams; the divergent light emitted by the source can be directly focused, and even if more than half of the beam is lost, it's sufficient for subsequent diffraction. However, extreme ultraviolet (EUV) light differs from visible light. EUV sources emit weaker light that is easily absorbed, and even a small loss during focusing can render the light unusable, requiring maximum collection. However, in visible light optics, collimation before focusing the beam necessitates adding a lens, which is not only difficult to assemble but also increases the overall size. Therefore, beams are generally focused directly without collimation, and similarly, collimation is not considered for EUV. Furthermore, due to its easily absorbed nature, EUV cannot pass through lenses, and those skilled in the art would not consider collimating it, but rather focus it directly into converging light. Therefore, the industry suffers from a coupling problem: low efficiency due to shadowing effects caused by the converging light entering the grating, and low resolution due to aberrations.

[0028] In practical applications, complex variable-spacing gratings or combinations of multiple optical elements are required to correct aberrations, resulting in complex system structures, high costs, and significant alignment difficulties. Moreover, the pulse broadening is significant, making it difficult to meet the needs of ultrafast dynamics research at the femtosecond and attosecond scales.

[0029] See Figures 1-3As shown in the figure, an extreme ultraviolet high-resolution monochromatic method provided by an embodiment of the present invention is characterized by comprising the following steps: S1 provides an incident light source that emits Gaussian extreme ultraviolet laser with a divergence angle.

[0030] The light source is one of the following: DPP light source, LPP light source, single-mode laser, or spectral correction lamp (ultra-low pressure, low temperature spectral correction lamp). These are commonly used point light sources or discrete point light sources.

[0031] S2. Set an off-axis parabolic reflector as a collecting mirror 1. The collecting mirror 1 receives the extreme ultraviolet light beam and collimates it into parallel light.

[0032] An off-axis parabolic mirror is a key aspherical optical element whose reflecting surface is a portion of a rotationally symmetric parent parabola that does not contain the axis of symmetry. Based on the geometric properties of a parabola, all collimated beams incident parallel to the optical axis of the parent parabola will converge aberration-free at the focal point after reflection. Conversely, when placed at a point source and the focal point, they can be collimated into high-quality parallel light. This reflective working principle fundamentally avoids chromatic aberration and eliminates the spherical aberration inherent in spherical mirrors, enabling diffraction-limited beam manipulation in the ultraviolet, visible, infrared, and even terahertz wavelength ranges.

[0033] Therefore, by using the collecting mirror 1, the discrete linear beam emitted by the light source can be collimated into a parallel beam. Compared with the existing technology that directly converts the discrete beam into a converging beam by focusing, the collimation function of the off-axis parabolic mirror can convert the divergent light emitted by the point light source into a parallel beam without divergence or angle difference. It can also allow more beams to enter the subsequent grating through collimation, and the distance change of the parallel beam will not affect the beam shape.

[0034] However, if the divergent light is directly focused into a converging light without collimation by adjusting the off-axis degree of the off-axis parabolic mirror, the reflecting surface of the off-axis parabolic mirror needs to be enlarged accordingly based on the size of the reflected spot, i.e., its effective aperture needs to be increased. This increases the cost. Furthermore, the light spot with a divergent angle incident on different positions of the off-axis parabolic mirror will produce spherical aberration at the subsequent slit 4 due to the different incident angles, causing the light spot at the slit to diffuse. Moreover, the edges of the large diffused light spot are blurred, and less effective light passes through slit 4, with more energy being blocked. Furthermore, the converging light incident on the subsequent grating 2 will inevitably diverge (either the converging light enters the grating 2 before reaching the focal point, or the converging light converges to the focal point and then diverges before entering the grating; in both cases, the grating 2 essentially receives diverging light). Since the incident angles of beams at different heights are not uniform (i.e., the beam aperture and angle are uncontrollable), the beam splitting of the grating 2 will be inconsistent, leading to a decrease in resolution. Moreover, the inconsistent incident angles at different points on the grating 2 will disrupt the conical diffraction condition. Therefore, this application abandons the method used in the prior art of directly focusing the diverging light into a converging light incident on the grating 2, and instead collimates the diverging light before incident, overcoming this technical bias.

[0035] Furthermore, off-axis parabolic mirrors can capture more light beams. Since the extreme ultraviolet light emitted by the light source diverges at a large angle, direct focusing can only capture a small central beam. Off-axis parabolic mirrors, with their large aperture and large solid angle, can collect and converge the originally divergent light, transforming it into parallel light. The collimated parallel light maintains its cross-sectional size throughout its path and is entirely delivered to grating 2, significantly improving energy utilization. Moreover, after the divergent light enters grating 2, only the central portion satisfies the diffraction condition, resulting in parallel light incidence. The entire top surface of grating 2 is uniformly illuminated, effectively improving beam utilization.

[0036] S3. A grating 2 is set up to split the parallel light. The grating 2 is a reflective plane grating. The parallel light collimated by the collecting mirror 1 is incident on the grating 2 at a preset angle along the grating 2 etch line direction to form conical diffraction. The grating 2 is rotated to adjust the incident azimuth angle α of the parallel light so that extreme ultraviolet light of different wavelengths propagates along different diffraction azimuth angles β.

[0037] The preset angle for the incident parallel light after collimation by the collecting mirror 1 is a small angle. When applied to conical diffraction in the extreme ultraviolet band, the range of this small angle γ (the angle between the beam and the grating 2 scribe plane) is -6° to 6°. In this embodiment, γ is selected as 6°.

[0038] Conical diffraction satisfies the grating propagation equation: ; in, m is the diffraction order; λ is the wavelength; σ is the grating constant, which is the reciprocal of the number of grating lines (1 / n), and n is the number of grating lines per millimeter, which is a dimensionless number; γ is the angle between the beam and the plane of the grating 2 scribe line; α is the incident azimuth angle, which is the angle between the projection of the incident ray onto the plane perpendicular to the grating 2 groove and the normal to the grating 2. β is the diffraction azimuth angle, which is the angle between the projection of the diffracted ray onto the plane perpendicular to the grating 2 and the normal to the grating 2.

[0039] See Figures 5-6 As shown, in this embodiment, based on the grating propagation equation, the diffraction angles of different wavelengths after being split by the grating 2 can be calculated, thereby deducing the linear dispersion of the system. In use, by rotating the angle of the grating 2, that is, by adjusting the tilt angle of the grating 2 to adjust the incident azimuth angle α, the diffraction azimuth angle β can be controlled, so that the monochromatic light of the target wavelength is incident on the center of the focusing lens 3.

[0040] See Figure 7 As shown, it should be noted that the spectral width of a continuous spectrum is limited, such as "white light". Theoretically, a continuous spectrum should include all wavelengths, but in practice it is often a segment of the full spectrum. Sometimes a segment of a continuous spectrum may only be a line spectrum composed of a few spectral lines with a linewidth of 1 nm. For example, with DPP or LPP light sources, different β angles can allow different monochromatic lights to be incident on the center of focusing lens 3, thereby separating the different monochromatic lights.

[0041] S4. Set an off-axis parabolic reflector as a focusing mirror 3 and adjust the distance between the focusing mirror 3 and the grating 2 to adjust the linear dispersion. A slit 4 is set on one side of the focusing mirror 3. The focusing mirror 3 receives the monochromatic parallel light after conical diffraction by the grating 2 and focuses it to the slit 4, so that the monochromatic parallel light forms monochromatic light and the monochromatic light exits from the slit 4.

[0042] Based on the explanation of the principle of the off-axis parabolic reflector in step S2, it can be concluded that the focusing lens 3 can focus the required monochromatic light to the slit 4 and reduce the light plate area of ​​the adjacent monochromatic beam at the focal point, thereby increasing the resolution.

[0043] The collecting mirror 1 has an incident angle of 84°, a focal length of 300nm, and is coated with a gold film (Au film). The focusing mirror 3 has an incident angle of 84°, a focal length of 1000nm, and is also coated with a gold film.

[0044] See Figure 4 As shown, Figure 4This is a schematic diagram of the surface shape and beam propagation of an off-axis parabolic reflector with an incident angle of 90°. It can be seen that monochromatic parallel light can be focused at a point after being reflected by the focusing mirror 3. The slit 4 is located at the focal point F, so the focused monochromatic light can exit at the slit 4.

[0045] In this application, both the collecting mirror 1 and the focusing mirror 3 use off-axis parabolic mirrors with large-angle incident incidence. In this embodiment, the incident angle of both mirrors is 84°, but the angle needs to be adjusted under different usage conditions, and is generally close to 90° (i.e., a large angle). Both the collecting mirror 1 and the focusing mirror 3 are coated with a gold film. This is because when used in the extreme ultraviolet band, only large-angle incident incidence and a specific coating can ensure good reflection efficiency.

[0046] Specifically, when the incident angle is ≤10°, a reflector coated with a Mo-Si multilayer film is usually used, mainly applying the Bragg diffraction principle, with a reflectivity of greater than 65% and less than 70% in the 13.5nm band.

[0047] When the incident angle is greater than 80°, gold-plated or ruthenium-plated mirrors are usually used. A 30nm thick gold-plated or ruthenium-plated monolayer film has a reflectivity of greater than 80% for extreme ultraviolet radiation of 10nm~120nm at an incident angle of 87°.

[0048] Mo-Si multilayer films are more expensive, but they allow for narrower incident angles, making optical path adjustment easier. Single-layer metal films are cheaper, but require wider incident angles, making optical path adjustment slightly more difficult. Considering cost, gold-plated films are generally used in practical applications.

[0049] S5. Select monochromatic light of the target wavelength through slit 4.

[0050] In this embodiment, the system has a 50-micrometer slit 4 at the focal point of the focusing lens 3. To allow monochromatic light beams to pass through the slit 4, unwanted monochromatic light beams are blocked by filters on both sides of the slit 4, thus selecting monochromatic light of a specified wavelength for emission. The position of the slit 4 needs to be adjusted accordingly to select monochromatic light corresponding to different light spots.

[0051] In this embodiment, the method adopts an integrated process of collimation by collecting mirror 1 → conical diffraction and spectral dispersion by grating 2 → focusing by focusing mirror 3 → slit 4 for screening. Combined with a double off-axis parabolic reflector with large-angle incident light and gold-plated film, the method fundamentally avoids chromatic aberration and spherical aberration, ensuring high reflection efficiency in the extreme ultraviolet band.

[0052] The grating 2 employs conical diffraction, unlike conventional perpendicular incidence diffraction. For extreme ultraviolet light, selecting the light spot only requires adjusting the position of the slit 4 and the tilt angle of the grating 2, thus enabling the selection of monochromatic light in different wavelength bands. This method boasts high diffraction efficiency, uniform light spot distribution in the confocal plane, and ease of spot selection. Furthermore, by adjusting the distance between the focusing lens 3 and the grating 2, the beams of different wavelength bands can be further separated, thereby reducing linear dispersion and increasing resolution. This results in clearer spatial separation, more concentrated energy, and a more regular distribution of monochromatic light after beam splitting. The core of spectral resolution is the ability to distinguish adjacent wavelengths. The clear, concentrated, and regular light spot distribution in this application directly reduces interference from adjacent wavelengths, allowing the system to accurately identify and filter the target wavelength, thereby improving resolution from a practical application perspective.

[0053] Specifically, resolution refers to the monochromator's ability to distinguish between two spectral lines with very similar wavelengths. The criterion is that the separation distance between the two spectral lines' spots on the confocal plane must be greater than or equal to the slit width 4 (or half the width of the spot itself); otherwise, they will overlap and become indistinguishable. Because extreme ultraviolet light has extremely short wavelengths (typically 10nm-124nm), low energy, and is easily absorbed by the medium, it can only operate through reflective optical systems. Furthermore, its diffraction angle is extremely sensitive to wavelength (the difference in diffraction angles between adjacent wavelengths is minimal). If the spot distribution is disordered and the energy is dispersed, it will directly lead to the overlap of spots of adjacent wavelengths. Conventional perpendicular incidence (traditional in-plane diffraction) suffers from significant shadowing effects and irregular spot distribution.

[0054] Among these issues, the shadowing effect is significant, meaning that extreme ultraviolet light requires a small grazing angle of incidence. In traditional diffraction geometry, the grating grooves block the reflected light from adjacent grooves, resulting in dispersed spot energy and blurred edges (leading to a trailing effect). The irregular spot distribution means that the incident and diffracted light are coplanar, and diffracted spots of adjacent wavelengths partially overlap, with uneven energy distribution (weak at the center and scattered at the edges), making it difficult to accurately locate the center of the spot for the target wavelength.

[0055] The conical diffraction method described in this application offers the advantage of easy spot selection. Firstly, it concentrates the spot energy. By aligning the grooves of grating 2 parallel to the optical axis, conical diffraction significantly reduces shading effects, allowing incident light energy to be efficiently focused onto the target diffraction order, forming a compact spot with a bright center and sharp edges, rather than a scattered, diffuse spot. Secondly, it makes the spatial separation of the spot clearer. The geometric configuration of conical diffraction allows diffraction spots of different wavelengths to be regularly arranged along a fixed direction (perpendicular to the grating 2's groove plane). The separation distance between adjacent wavelengths (e.g., 10nm and 10.03nm) on the confocal plane is clear, with no overlap or tailing. Furthermore, it allows for more precise spot positioning. The spot distribution is uniform and regular, making it extremely easy to align the center of the target wavelength spot with the optical axis of focusing lens 3 and the center of slit 4. No complex adjustments are needed to ensure the target spot passes completely through the slit without being truncated by the slit's edge.

[0056] See Figures 2-6 As shown, the embodiment of the present invention provides an extreme ultraviolet high-resolution monochromatic system, which is applicable to the extreme ultraviolet high-resolution monochromatic method described above.

[0057] This extreme ultraviolet high-resolution monochromatic system requires a light source capable of emitting Gaussian extreme ultraviolet laser. The extreme ultraviolet high-resolution monochromatic system includes, in sequence along the optical path of the extreme ultraviolet laser, a collecting mirror 1, a grating 2, a focusing mirror 3, and a slit 4.

[0058] Both the collecting mirror 1 and the focusing mirror 3 are off-axis parabolic mirrors. The collecting mirror 1 is used to collimate the diverging extreme ultraviolet laser into parallel light, and the focusing mirror 3 is used to focus the parallel light.

[0059] Grating 2 is used to split parallel light using conical diffraction.

[0060] In this embodiment, the light source emits Gaussian extreme ultraviolet laser light with a divergence angle. After traveling a certain distance, it is reflected by the collecting mirror 1. At this time, the light source is located at the focal point of the off-axis parabolic mirror (collecting mirror 1), so the collecting mirror 1 shapes the light with the beam expansion angle into collimated parallel light. After the parallel light illuminates the planar grating 2, the grating 2 separates the light of different wavelengths, and at this time, the grating 2 uses conical diffraction for beam splitting. The grating 2 separates the beams of different wavelengths, at which point the beams are monochromatic and will propagate in different directions. After beam splitting, the focusing mirror 3 focuses the monochromatic light (as required) after beam splitting by the grating 2. Since the exit angle of the monochromatic light of each wavelength is different after beam splitting, after being focused by the off-axis parabolic mirror (focusing mirror 3), the light of different wavelengths can be separated at the slit 4, achieving high linear dispersion.

[0061] Optionally, the collecting mirror 1 has an incident angle of 84°, a focal length of 300nm, and a gold coating on its surface. The focusing mirror 3 has an incident angle of 84°, a focal length of 1000nm, and a gold coating on its surface. The grating 2 is a reflective planar grating with 1200 lines / mm, and the groove direction of the grating 2 is parallel to the optical axis.

[0062] In this embodiment, both the collecting mirror 1 and the focusing mirror 3 use off-axis parabolic mirrors with large-angle incident incidence. The incident angle of both mirrors is 84°, but the angle needs to be adjusted under different operating conditions, generally approaching 90° (i.e., a large angle). Both the collecting mirror 1 and the focusing mirror 3 are coated with a gold film. This is because, under extreme ultraviolet (EUV) conditions, only large-angle incident incidence and a specific coating can ensure good reflection efficiency, achieving a balance between performance and cost while ensuring full beam coverage. The groove direction of the grating 2, parallel to the optical axis, is the core structural basis of conical diffraction, ensuring the conical propagation of the diffracted beam and providing structural protection for minimizing shadowing effects and maximizing diffraction efficiency.

[0063] Optionally, the distance from the focusing lens 3 to the slit 4 is the equivalent exit focal length L. B The linear dispersion of the system is proportional to cosβ and proportional to L. B The diffraction order m and the line density n are inversely proportional.

[0064] Where β is the diffraction azimuth angle.

[0065] In this embodiment, the calculations involved in the system are mainly two: system energy utilization rate and linear dispersion calculation.

[0066] The system utilization rate is calculated as follows: Collection efficiency = Reflection efficiency of collecting mirror 1 × Solid angle / 2π.

[0067] Overall system efficiency = Collection efficiency of collecting mirror 1 × Diffraction efficiency of grating 2 × Reflection efficiency of focusing mirror 3

[0068] The reflection efficiency of collecting mirror 1 is affected by its angle and surface coating, and the reflection efficiency of focusing mirror 3 is similarly affected. The SI unit for solid angle (symbol Ω) is steradian (sr). Its geometric definition is: the projected area A intercepted by the aperture of an off-axis parabolic mirror on a sphere of radius r, centered at a point light source (i.e., the observation point), divided by the square of the sphere's radius r. 2 The resulting value is the solid angle, i.e., Ω = A / (r 2 This can be compared to the fact that a plane angle is the arc length of a unit circle, while a solid angle is the area of ​​a unit sphere.

[0069] Linear dispersion is defined as the spectral width per unit length along the spectral spread direction on the focal plane, measured in nm / mm. Taking two spectrometers with different linear dispersions as an example, one might spread a 0.1 nm wide spectrum to 1 mm, while the other might spread a 10 nm wide spectrum to 1 mm. It's easy to imagine that finer spectral information is more easily obtained with the first spectrometer than the second. Compared to the high dispersion of the first spectrometer, the second spectrometer is called a low-dispersion instrument. Linear dispersion reflects a spectrometer's ability to resolve fine spectral details.

[0070] The linear dispersion of wavelength λ in the direction perpendicular to the diffracted beam can be derived and corrected using the following formula: .

[0071] Specifically, for the equation of the conical diffraction grating Differentiating both sides, we obtain the azimuth dispersion of conical diffraction (the change in azimuth angle caused by a unit wavelength change), as shown in the following formula: .

[0072] This formula differs from the traditional character dispersion formula. In comparison, the denominator includes a sinγ factor. Since the value of γ is very small in the EUV / soft X-ray band (γ is 6° in this embodiment, sinγ=0.1), this also greatly improves the angular dispersion capability of conical diffraction, which is 1 / sinγ times that of traditional geometry.

[0073] From line dispersion to character dispersion, line dispersion The description focuses on how wavelength is converted into spatial displacement on the detector plane (confocal plane), which requires a clear understanding of how azimuth changes dβ are mapped to dx.

[0074] In this application, in the globally optimized and aberration-corrected optical system (i.e., the extreme ultraviolet high-resolution monochromatic system), this mapping relationship is determined by the optical path after diffraction by grating 2. Assuming that after aberration correction, the displacement dx on the confocal plane and the azimuth change dβ are related through an effective focal length F_{eff} (i.e., dx ≈ F_{eff}·dβ), then the formula for linear dispersion can be derived. That is, the linear dispersion formula... Substituting dx≈F_{eff}·dβ, we can derive dx≈F_{eff}·(m / (σsinycosβ))·dλ, and after simplification, we get: .

[0075] Considering unit conversion, dλ is commonly measured in nanometers (nm), dx in millimeters (mm), and σ in millimeters (mm). Introducing the grating line density n (lines / mm), and σ as 1 / n, the final formula is: .

[0076] In the formula: F eff The equivalent exit focal length is expressed in mm. dx represents the unit interval, in mm.

[0077] The other parameters are explained elsewhere in the text.

[0078] In this extreme ultraviolet high-resolution monochromatic system, F eff Let F be the distance from focusing lens 3 to exit slit 4. Therefore, linear dispersion is proportional to cosβ and sinγ, and related to the exit focal length F. eff The linear dispersion is inversely proportional to parameters such as the diffraction order m and the line density n. This further reveals the relationship between linear dispersion and these parameters, providing theoretical support for optimizing the linear dispersion of the system. The equivalent exit focal length F can be adjusted according to practical application requirements. eff By adjusting the diffraction order m or the line density n, the linear dispersion performance can be flexibly controlled, enhancing the adaptability of the system and making it suitable not only for extreme ultraviolet lasers.

[0079] In some embodiments, when the grating 2 is concave, F eff This is the distance from grating 2 to exit slit 4.

[0080] Optionally, the slit 4 is located at the focal point of the focusing lens 3 to filter the target monochromatic light, and the width of the slit 4 is 50 micrometers.

[0081] In this embodiment, the 50-micrometer-wide exit slit 4 is precisely aligned with the focal point of the focusing lens 3, achieving efficient screening of the target monochromatic light.

[0082] In this invention, two off-axis parabolic mirrors are used before and after the grating 2, namely a collecting mirror 1 and a focusing mirror 3. The collecting mirror 1 can convert the divergent light emitted from the point source into parallel light, which then illuminates the grating 2, thus increasing energy utilization. The grating 2 adopts a conical diffraction method, which greatly increases the diffraction efficiency in the extreme ultraviolet band. Since the beam is shaped into parallel, non-divergent collimated light by the first off-axis parabolic mirror (collecting mirror 1), the beam after conical diffraction by the grating 2 is still parallel, non-divergent collimated light. Therefore, it can be focused into a small spot of 10μm by the focusing mirror 3 at the rear, and the aberration is small at this time. At the focal point of the focusing mirror, the selected monochromatic beam can be filtered out by the slit 4.

[0083] The core difference between conical diffraction (out-of-plane diffraction) and conventional diffraction (classical in-plane diffraction) lies in their geometric configuration. Conical diffraction sets the direction of the grooves in grating 2 parallel to the optical axis, making the incident light and the diffracted light non-coplanar, forming a cone-shaped diffracted beam. Conventional diffraction, on the other hand, requires the incident light, the normal to grating 2, and the diffracted light to be coplanar, and the grooves to be perpendicular to the incident plane. This leads to a severe shadowing effect, where one groove in grating 2 blocks the reflected light from adjacent grooves, resulting in a significant loss of photons. This key difference gives conical diffraction a significant advantage in the extreme ultraviolet-soft X-ray band: it can greatly reduce the shadowing effect at low grazing angles, allowing the incident light to more effectively illuminate each groove of grating 2, laying the foundation for high efficiency, increasing the theoretical diffraction efficiency to over 90%, and allowing the use of uniformly spaced gratings. Combined with a simple rotating off-axis parabolic mirror to adjust the angle with the incident light direction (single degree of freedom), global aberration correction can be achieved. At the same time, because both collecting mirror 1 and focusing mirror 3 use off-axis parabolic mirrors, the pulse broadening caused by the transmission element can be reduced, which is far superior to traditional diffraction methods.

[0084] In some embodiments, grating 2 is a blazed grating, the grooves of which are designed with a specific sawtooth shape (blaze angle ψ). The purpose is to cause specular reflection of light at each groove, thereby concentrating most of the light energy onto a specific diffraction order, rather than dispersing it evenly across all orders. Under conical diffraction geometry, the condition for grating efficiency to reach its maximum is described by the following formula: α+β=2ψ; Where α and β are the incident and diffracted azimuth angles, respectively, and ψ is the blaze angle of the grating. When the optical path satisfies this condition, both the incident and diffracted light satisfy the specular reflection condition relative to the reflecting surface of a single groove, thereby maximizing efficiency.

[0085] Optimal condition: combination of Littrow configuration and aberration correction.

[0086] The highest possible efficiency can be achieved when both of the following conditions are met: α=β=ψ=2Δ; This is essentially a combination of the Littrow condition (a diffraction configuration where light returns along its original path) and the aforementioned aberration correction angle Δ. Under this configuration, not only is the shading effect minimized (because α=ψ), but the grating is also in its most brilliant state as designed, while the system remains aberration-free.

[0087] In this embodiment, a DPP light source is used as the starting point for the simulation. This system can separate 10nm and 10.03nm light by 35 micrometers. When slit 4 is 50 micrometers wide and 10nm light is located at the center of slit 4, 10.03nm light will not affect the resolution. According to the linear dispersion calculation method, the linear dispersion of the monochromatic system at this time can be obtained as 0.857nm / mm, the collection efficiency of collecting mirror 1 is 2.31E-4, and the total system efficiency is 3.22E-5.

[0088] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for high-resolution extreme ultraviolet monochromaticization, characterized in that, Includes the following steps: S1. Provides an incident light source that emits Gaussian extreme ultraviolet laser with a divergence angle; S2. An off-axis parabolic reflector is set as a collecting mirror (1). The collecting mirror (1) receives the extreme ultraviolet light beam and collimates it into parallel light. S3. A grating (2) is set up to split the parallel light. The grating (2) is a reflective plane grating. The parallel light collimated by the collecting mirror (1) is incident on the grating (2) at a preset angle along the grating (2) etched direction to form conical diffraction. The grating (2) is rotated to adjust the incident azimuth angle α of the parallel light so that extreme ultraviolet light of different wavelengths propagates along different diffraction azimuth angles β. S4. Set an off-axis parabolic reflector as a focusing mirror (3) and adjust the distance between the focusing mirror (3) and the grating (2) to adjust the linear dispersion. A slit (4) is provided on one side of the focusing mirror (3). The focusing mirror (3) receives the monochromatic parallel light after conical diffraction by the grating (2) and focuses it to the slit (4) so ​​that the monochromatic parallel light forms monochromatic light and the monochromatic light exits from the slit (4). S5. Select monochromatic light of the target wavelength through the slit (4).

2. The extreme ultraviolet high-resolution monochromaticization method as described in claim 1, characterized in that, In S1, the light source is one of a DPP light source, an LPP light source, a single-mode laser, or a spectral correction lamp.

3. The extreme ultraviolet high-resolution monochromaticization method as described in claim 1, characterized in that, In S3, conical diffraction satisfies the grating propagation equation: ; in, m is the diffraction order; λ is the wavelength; σ is the grating constant; γ is the angle between the beam and the grating (2) scribe plane; α is the incident azimuth angle; β is the diffraction azimuth angle.

4. The extreme ultraviolet high-resolution monochromaticization method as described in claim 1, characterized in that, In S3, the diffraction azimuth angle β is controlled by adjusting the incident azimuth angle α, so that the monochromatic light of the target wavelength is incident on the center of the focusing mirror (3) to separate different monochromatic lights.

5. An extreme ultraviolet high-resolution monochromatic system, applicable to the extreme ultraviolet high-resolution monochromaticization method as described in any one of claims 1-4, characterized in that, The extreme ultraviolet high-resolution monochromatic system includes: a collecting mirror (1), a grating (2), a focusing mirror (3) and a slit (4) arranged sequentially along the optical path of the extreme ultraviolet laser. The collecting mirror (1) and the focusing mirror (3) are both off-axis parabolic reflectors. The collecting mirror (1) is used to collimate the diverging extreme ultraviolet laser into parallel light, and the focusing mirror (3) is used to focus the parallel light. The grating (2) is used to split parallel light by conical diffraction.

6. The extreme ultraviolet high-resolution monochromatic system as described in claim 5, characterized in that, The collecting mirror (1) has an incident angle of 84°, a focal length of 300nm, and a gold film on its surface.

7. The extreme ultraviolet high-resolution monochromatic system as described in claim 5, characterized in that, The focusing lens (3) has an incident angle of 84°, a focal length of 1000nm, and a gold film on its surface.

8. The extreme ultraviolet high-resolution monochromatic system as described in claim 5, characterized in that, The grating (2) is a reflective planar grating with a grating line count of 1200 lines / mm and the groove direction of the grating (2) is parallel to the optical axis.

9. The extreme ultraviolet high-resolution monochromatic system as described in claim 5, characterized in that, The distance from the focusing lens (3) to the slit (4) is the equivalent exit focal length L. B The linear dispersion of the system is proportional to cosβ and proportional to L. B The diffraction order m is inversely proportional to the line density n; Where β is the diffraction azimuth angle.

10. The extreme ultraviolet high-resolution monochromatic system as described in claim 5, characterized in that, The slit (4) is located at the focal point of the focusing lens (3) and is used to filter target monochromatic light. The width of the slit (4) is 50 micrometers.

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