A short-wavelength coherent-permissive imaging system based on planar optical elements

Abstract

This invention relates to the field of optical imaging technology, specifically to a short-wavelength coherence-tolerant imaging system based on planar optical elements. The key technical features include: an incident light source; a multi-segment planar reflector for splitting the short-wavelength beam into multiple primary sub-beams; a multi-stage semi-transparent beam-splitting reflector, through which the multiple primary sub-beams sequentially pass along their respective propagation directions to further decompose each primary sub-beam into multiple sub-beam components; an optical path correction reflector, with each sub-beam component correspondingly positioned to guide it to a target surface; and a target surface where the sub-beam components are superimposed to form an interference pattern, thereby achieving imaging. This invention, through multi-stage beam splitting and precise optical path correction, enables multiple sub-beams to achieve equivalent phase superposition under low-coherence short-wavelength conditions, thereby achieving stable, high-contrast, and scalable interferometric imaging in the extreme ultraviolet band.

Description

Technical Field

[0001] This invention relates to the field of optical imaging technology, and more specifically to a short-wavelength coherent-allowed imaging system based on planar optical elements. Background Technology

[0002] With the rapid development of semiconductor manufacturing, ultra-large-scale integrated circuit testing, nanomaterial characterization and biomolecular imaging, the scientific community's requirements for the spatial resolution of optical imaging have entered the nanoscale. According to the Rayleigh criterion, the most direct way to improve resolution is to shorten the imaging wavelength. Therefore, imaging systems are gradually evolving from visible light and ultraviolet light to extreme ultraviolet (EUV) and even shorter wavelengths.

[0003] However, in the short-wavelength region below 200nm (especially the 50nm to 200nm band), existing imaging technologies face the following challenges: First, almost all traditional transmission optical materials exhibit extremely strong absorption characteristics in this wavelength band, causing conventional refractive lens systems to completely fail. Second, short-wavelength imaging often relies on total internal reflection aspherical mirrors or complex multilayer film structures. These systems not only require extremely high processing precision and are difficult to assemble and adjust, but are also bulky, making it difficult to achieve miniaturization and low-cost widespread adoption. Finally, traditional interferometric imaging systems usually require light sources with extremely high coherence. However, high-performance, high-coherence short-wavelength light sources are extremely expensive, complex to maintain, and scarce in resources. Meanwhile, relatively readily available miniaturized short-wavelength light sources typically have coherence lengths on the order of centimeters, making it difficult to form stable interferometric imaging in conventional systems. Therefore, there is an urgent need for a system that uses only easily fabricated planar optical elements and can achieve high-resolution imaging under low coherence conditions. To solve the above problems, this application proposes a short-wavelength coherence-tolerant imaging system based on planar optical elements. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a short-wavelength coherent permissive imaging system based on planar optical elements, thus solving the problems mentioned in the background art.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A short-wavelength coherent-permissive imaging system based on planar optical elements, comprising: Incident light source, used to provide short-wavelength light beams; A multi-segment planar reflector is used to separate the short-wavelength beam into multiple primary sub-beams; A multi-stage semi-transparent beam splitter is used to further decompose each primary sub-beam into multiple sub-beam components by passing through the multi-stage semi-transparent beam splitter sequentially along their respective propagation directions. An optical path correction mirror is provided for each of the sub-beam components. It is used to adjust the propagation optical path of the corresponding sub-beam component and guide it to the target surface. The mirror position of each optical path correction mirror can be adjusted independently to provide the required phase for each interference beam. The sub-beam components are superimposed on the target surface to form an interference pattern, thereby achieving imaging; The characteristic is that any two of the sub-beam components satisfy the following optical path difference condition at the target surface: in, Let be the optical path difference between any two sub-beam components. The longitudinal coherence length of the incident light source.

[0006] Preferably, the multi-segment planar reflector is arranged in an oblique incidence manner so that the incident beam acts on multiple reflection zones respectively and outputs multiple primary sub-beams with different propagation directions, thereby maintaining the structural symmetry of the system.

[0007] Preferably, the multi-stage semi-transparent beam-splitting mirror is a planar thin-film mirror.

[0008] Preferably, the reflectivity and transmittance of the planar thin-film reflector are configured according to a preset beam splitting ratio to balance the energy contribution of each sub-beam component at the target surface.

[0009] Preferably, the optical path correction mirror is an adjustable plane mirror.

[0010] Preferably, the adjustable plane mirror achieves optical path compensation through nanometer-level displacement adjustment, so that when different sub-beam components reach the target surface, the optical path difference is less than the longitudinal coherence length of the incident light source, and the sub-beam components satisfy the phase relationship required by the interference pattern.

[0011] Preferably, the wavelength of the short-wavelength light beam is between 50 nm and 200 nm.

[0012] Preferably, the longitudinal coherence length of the incident light source is on the order of centimeters.

[0013] Preferably, the system expands the imaging of large-aperture beams and large-area targets by increasing the number of stages of the multi-stage semi-transparent beam-splitting mirrors.

[0014] In summary, the present invention has the following main beneficial effects: 1. This invention constructs the optical path using all-planar optical elements, effectively avoiding the strong absorption limitation of traditional transmissive materials in the short wavelength region, and realizing extreme ultraviolet imaging with wavelengths as low as 50nm. This all-planar design not only simplifies the system structure and improves the working stability, but also gives it good scalability, and can be effectively applied to the high-resolution imaging needs of large-aperture short-wavelength beams and large-area target surfaces.

[0015] 2. This invention relies on the synergistic effect of multi-stage semi-transparent beam splitting and optical path correction mirrors to precisely adjust the propagation optical path of each sub-beam component, ensuring that it meets the optical path difference and phase consistency conditions at the target location, and achieving equivalent phase superposition. This mechanism significantly reduces the stringent requirements of the system on the coherence of the light source, enabling it to form stable interferometric imaging even with a longitudinal coherence length on the order of centimeters, greatly improving the practicality and light source compatibility of short-wavelength imaging systems. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall system structure of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of protection of the present invention. The conditions in the embodiments can be further adjusted according to specific conditions, and simple improvements to the method of the present invention under the premise of the concept of the present invention are all within the scope of protection claimed by the present invention.

[0019] Example 1 In this embodiment, a short-wavelength coherence-tolerant imaging system based on planar optical elements is provided to verify the basic imaging feasibility of the system under centimeter-level longitudinal coherence length conditions. The system is suitable for short-wavelength beams with a center wavelength of 95 nm and a longitudinal coherence length of the incident light source. Set it to 1.5cm.

[0020] The system includes an incident light source, a multi-segment plane mirror, a multi-stage semi-transparent beam splitter mirror, an optical path correction mirror, and a target surface. The 95nm short-wavelength beam emitted by the incident light source first illuminates the multi-segment plane mirror, which separates the incident beam into multiple primary sub-beams. The multiple primary sub-beams then enter the multi-stage semi-transparent beam splitter mirror along their respective propagation paths.

[0021] Multi-stage semi-transparent beam-splitting mirrors are arranged sequentially along the beam propagation direction. In this embodiment, a two-stage beam-splitting structure is adopted, so that each primary sub-beam passes through two stages of planar thin-film mirrors in sequence and is further decomposed into multiple sub-beam components, thereby forming a multi-stage spatially separated beam array. Each stage of planar thin-film mirrors realizes the distribution of reflection and transmission through the thin-film layer system to meet the beam splitting requirements in the 95nm band.

[0022] Each sub-beam component is equipped with an optical path correction mirror during propagation. The optical path correction mirror adopts an adjustable plane mirror structure and is installed on an adjustable displacement mechanism. By changing the geometric optical path of the corresponding optical path through displacement along the beam propagation direction, the propagation path of each sub-beam component can be finely adjusted.

[0023] In the initial state of the system, due to differences in the structure of each optical path and assembly errors, there is an initial optical path difference between different sub-beam components. In order to achieve stable interferometric imaging, each optical path correction mirror is adjusted one by one. During the adjustment process, the interference fringes formed at the target surface are used as feedback basis. By observing the changes in the clarity and contrast of the fringes, each optical path correction mirror is initially aligned and repeatedly fine-tuned.

[0024] Through the above adjustments, the optical path difference between any two sub-beam components is reduced. The size is gradually reduced and controlled within a preset range; in this embodiment, it is adjusted to approximately 0.2 cm to meet the requirements. ,in Let be the optical path difference between any two sub-beam components. The longitudinal coherence length of the incident light source is given. Furthermore, the phase of each beam can be individually adjusted by its respective reflector, so that the predefined phase relationship can be reliably satisfied on the target surface.

[0025] After the above adjustments were completed, the interference pattern formed at the target surface had high contrast and good stability, and could clearly reflect the structural information of the target. This result shows that under the conditions of a short wavelength of 95 nm and a longitudinal coherence length on the order of centimeters, the multi-path optical path difference can be effectively compensated by the synergistic effect of multi-segment beam splitting, multi-level beam splitting and optical path correction mirrors, thus achieving stable coherent permissible imaging.

[0026] Therefore, this embodiment verifies the technical feasibility of the present invention in achieving short-wavelength imaging under low coherence conditions, and provides a foundation for subsequent applications with shorter wavelengths and large-scale expansion.

[0027] Example 2: The basic structure and working principle of this embodiment are basically the same as those of Embodiment 1, except that: In this embodiment, the center wavelength of the incident light source is set to 50nm to verify the system's adaptability under shorter wavelength extreme ultraviolet conditions. Considering that the material absorption is significantly enhanced in this band, the multi-segment planar reflector is arranged in a grazing incidence manner so that the incident beam acts on the reflective surface at a small incident angle of 5 to 15 degrees, thereby improving the reflection efficiency and reducing energy loss.

[0028] Meanwhile, during optical path adjustment, the phase becomes more sensitive to changes in optical path due to the reduced wavelength. Therefore, the optical path correction mirror is adjusted more precisely to ensure that the components of each sub-beam still satisfy the following: This ensures that, under short wavelength and strong absorption conditions, each sub-beam component can still form a stable interference pattern at the target surface, as well as the predefined phase relationship.

[0029] This embodiment demonstrates that the present invention can still achieve stable imaging under extreme ultraviolet band conditions through a full-plane reflection structure and optical path correction mechanism, and has good short wavelength adaptability.

[0030] Example 3: The basic structure and working principle of this embodiment are basically the same as those of Embodiment 1, except that: In this embodiment, the incident light source is a large-aperture collimated short-wavelength beam, and its longitudinal coherence length is reduced to about 0.5 cm to simulate a larger field of view and lower coherence conditions.

[0031] In terms of beam splitting structure, the multi-stage semi-transparent beam splitter mirror adopts a three-stage or four-stage beam splitting structure, which further decomposes the primary sub-beam into more sub-beam components, forming an array of 64 or more sub-beam components to achieve coverage of a large area target surface.

[0032] Simultaneously, multiple sets of optical path correction mirrors are set up, and the positions of each optical path correction mirror are adjusted independently to ensure that the expanded multipath beam still satisfies the following: This enables the realization of equivalent phase superposition within a large area of ​​the target surface, as well as the design of the predefined phase relationship.

[0033] This embodiment demonstrates that the present invention can achieve large-area imaging without improving the coherence of the light source by increasing the number of spectral order and optical path correction units, and has good scalability.

[0034] Example 4: The basic structure of this comparative example is basically the same as that of Example 1, except that: no optical path correction reflector is set.

[0035] In this case, due to assembly and adjustment errors and path differences, a large optical path difference occurs between the sub-beam components, thus satisfying: This results in a significant decrease in the coherence between the sub-beam components, and the predefined phase relationship cannot be satisfied. Therefore, the sub-beam components cannot form a stable interference pattern at the target surface, which manifests as blurred or even disappeared interference fringes, resulting in a significant decrease in imaging quality.

[0036] Therefore, optical path correction mirrors and their corresponding optical path compensation mechanisms are essential technical features for achieving stable interferometric imaging.

[0037] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that, unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense as understood by one of ordinary skill in the art to which this invention pertains, and terms such as including or comprising as used in this invention mean that the element or object preceding the word covers the element or object listed after the word and its equivalents.

[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A short wavelength coherent permissive imaging system based on planar optical elements, characterized in that, include: Incident light source, used to provide short-wavelength light beams; A multi-segment planar reflector is used to separate the short-wavelength beam into multiple primary sub-beams; A multi-stage semi-transparent beam splitter is used to further decompose each primary sub-beam into multiple sub-beam components by passing through the multi-stage semi-transparent beam splitter sequentially along their respective propagation directions. An optical path correction mirror is provided for each of the sub-beam components. It is used to adjust the propagation optical path of the corresponding sub-beam component and guide it to the target surface. The mirror position of each optical path correction mirror can be adjusted independently to provide the required phase for each interference beam. The sub-beam components are superimposed on the target surface to form an interference pattern, thereby achieving imaging; The characteristic is that any two of the sub-beam components satisfy the following optical path difference condition at the target surface: wherein, is the optical path difference between any two sub-beam components, is the longitudinal coherence length of the incident light source.

2. The system of claim 1, wherein, The multi-zone planar reflector is arranged in an oblique incidence manner so that the incident beam acts on multiple reflection zones and outputs multiple primary sub-beams with different propagation directions, thereby maintaining the structural symmetry of the system.

3. The system of claim 1, wherein, The multi-stage semi-transparent beam-splitting mirror is a planar thin-film mirror.

4. The system according to claim 3, characterized in that, The reflectivity and transmittance of the planar thin-film mirror are configured according to a preset beam splitting ratio to balance the energy contribution of each sub-beam component at the target surface.

5. The system according to claim 1, characterized in that, The optical path correction mirror is an adjustable plane mirror.

6. The system according to claim 5, characterized in that, The adjustable plane mirror achieves optical path compensation through nanometer-level displacement adjustment, so that when different sub-beam components reach the target surface, the optical path difference is less than the longitudinal coherence length of the incident light source, and the sub-beam components satisfy the phase relationship required by the interference pattern.

7. The system according to claim 1, characterized in that, The short-wavelength beam has a wavelength of 50 nm to 200 nm.

8. The system according to claim 1, characterized in that, The longitudinal coherence length of the incident light source is on the order of centimeters.

9. The system according to claim 1, characterized in that, The system expands the imaging capabilities of large-aperture beams and large-area targets by increasing the number of stages of the multi-stage semi-transparent beam-splitting mirrors.

Images