Pt-HSQ-based high-resolution X-ray Fresnel zone plate and preparation method thereof

Abstract

The invention belongs to the technical field of micro-nano processing, and particularly relates to a Pt-HSQ-based high-resolution X-ray Fresnel zone plate and a preparation method thereof. According to the X-ray Fresnel zone plate, a Pt-HSQ metal-inorganic material system is adopted, a diffraction structure with a large aspect ratio and Pt material quasi-periodic dense stripes specially needed by an X-ray zone plate lens is formed through electron beam lithography and an ALD process, and diffraction focusing from a soft X-ray wave band to a hard X-ray wave band and imaging with an amplification function are achieved. The wave zone plate has excellent mechanical stability, and the irradiation resistance and morphology retentivity of the wave zone plate under high-energy irradiation are remarkably improved. And high-resolution X-ray focusing elements with different energy wavebands and different focal lengths can be prepared according to geometric design and material selection of the wave zone plate. The lens is suitable for microscopic imaging, coherent diffraction imaging, X-ray spectrum, nanometer detection and other scenes of a synchrotron radiation or off-line laboratory X-ray light source, and has wide popularization value and application prospect.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano fabrication technology, specifically relating to a high-resolution X-ray Fresnel zone sheet based on Pt-HSQ and its preparation method. Background Technology

[0002] With the construction and operation of the fourth-generation synchrotron radiation source, the demand for high-resolution, high-efficiency X-ray focusing elements has grown rapidly. X-ray microscopy can perform non-destructive analysis of materials, life science samples, and microelectronic devices with nanometer-level spatial resolution, and is an important supporting tool for advanced light source experiments. However, China still mainly relies on imports for the core focusing element, the Fresnel zone plate (FZP), on which this technology depends. Domestically, there is no mature capability for manufacturing high-resolution zone plates, especially high-efficiency zone plates in the 5-30 nm linewidth, hard X-ray band (1-20 keV), which remain a technological gap.

[0003] In existing technologies, gold-plated zone plates are one of the mainstream solutions for hard X-ray focusing elements. They utilize electron beam lithography to define the pattern, and then fill the template with metal through electroplating to achieve a high-absorption-contrast line-ray structure. However, this method has significant limitations when fabricating structures with a resolution of 5-30 nm. First, the electroplating process is highly sensitive to the template morphology and gold ion diffusion behavior, easily leading to stress compression and uneven metal deposition, affecting the final linewidth accuracy and thickness consistency. Summary of the Invention

[0004] The purpose of this invention is to provide a high-resolution X-ray Fresnel zone sheet based on the Pt-HSQ system with good mechanical stability and repeatability, high linewidth accuracy and thickness consistency, and a method for its preparation.

[0005] This invention provides a high-resolution X-ray Fresnel zone plate based on Pt-HSQ. Utilizing a Pt-HSQ metal-inorganic material system, it forms a diffraction structure with a high aspect ratio and dense quasi-periodic fringes of Pt material, characteristic of X-ray zone plate lenses, through electron beam lithography and ALD processes. This enables diffraction focusing and magnified imaging across the soft to hard X-ray bands. The structure, from bottom to top, consists of: a silicon substrate, a diaphragm window, a photolithography template, and a working structure layer covering the template. The working structure layer is obtained by etching a pattern on the photolithography layer (i.e., obtaining template openings through electron beam exposure and development), followed by high-density material deposition using atomic layer deposition (ALD). Fresnel zone plates are positioned above the diaphragm window, with their working direction perpendicular to the window plane. They can diffract and modulate incident X-rays, including focusing, dispersion, or interference modulation. Based on template-assisted pattern definition and period doubling strategy, the fabricated devices have linewidths as small as 20 nm and structural heights exceeding 500 nm, achieving high-efficiency X-ray wavefront modulation under high-resolution conditions.

[0006] The photolithography layer (i.e., photoresist) uses a material with high transmittance to hard X-rays with energies greater than 1 keV. This material can undergo a cross-linking reaction after exposure to a high-energy electron beam, so as to be used for electron beam lithography and development. It remains stable at high temperatures of 100~300℃, so as to be used as a template for atomic layer deposition when the working material is a metal. This type of photoresist is usually a dielectric photolithography material, specifically HSQ (hydrogen silsesquioxane) containing Si. The template linewidth is 5-50 nm, and the period is 20-200 nm. The template thickness is positively correlated with the linewidth, with a thickness range of 350 nm~2000 nm. Smaller linewidths correspond to thinner templates, and larger linewidths correspond to thicker templates.

[0007] The working layer (i.e., the diffraction structure of the device) is grown by atomic layer deposition, using a material with a high refractive index difference for hard X-rays, specifically the noble metal Pt; the working layer deposition thickness is 1 ~ 100 nm.

[0008] In this invention, the high aspect ratio specifically refers to an aspect ratio of 1:1 to 1:60, preferably 1:10 to 1:60, more preferably 1:30 to 1:60, and even more preferably 1:50 to 1:60.

[0009] The diaphragm window is square, with a thickness of 100 ~ 500 nm and a side length of 1 ~ 5 mm.

[0010] The diaphragm window material includes, but is not limited to, silicon nitride, silicon dioxide, or silicon, with silicon nitride being preferred.

[0011] The high-resolution X-ray Fresnel zone plate achieves imaging at resolutions of 30 nm and 20 nm under 7.2 keV hard X-rays, respectively. The theoretical focusing efficiency for 30 nm resolution is 13.46%, and the measured focusing efficiency is 10.11%. The theoretical focusing efficiency for 20 nm resolution is 13.13%, and the measured focusing efficiency is 8.07%. For a Fresnel zone plate lens with a feature size of 10 nm, the theoretical focusing efficiency is 3.36%, and the measured focusing efficiency is 1.78%.

[0012] In this invention, the objects to be processed mainly include photolithographic templates and thin-film high aspect ratio structures formed by metal or dielectric deposition.

[0013] The specific steps of the method for preparing the Fresnel zone plate provided by the present invention are as follows: (1) Thin film windows were prepared on a silicon substrate using PECVD; (2) A photolithography template is formed on the thin film window; (3) The pattern of the diffraction structure is formed in the photolithography layer using electron beam lithography; (4) Develop the sample obtained in step (3) to obtain the template structure; (5) Atomic layer deposition is performed on the sample obtained in step (4) to grow a high depth working layer of the diffraction structure in the sidewall region of the template, thereby forming a diffraction-type micro-nano optical structure with a large aspect ratio.

[0014] Furthermore: In step (1), the thin film window is square, with a thickness of 100 ~ 500 nm and a side length of 1 ~ 5 mm.

[0015] In step (2), the photoresist thickness is 50 ~ 4000 nm and it is baked to harden. The baking temperature is 150 ~ 180℃ and the time is 1 ~ 30 min.

[0016] In step (3), the exposure base dose of the electron beam lithography is 500 ~ 8000 μC / cm², the exposure relative dose is 0.05 ~ 2; the developer ratio is TMAH:H2O = 1:3, the development temperature is 40 ~ 50 ℃, and the development time is 1 ~ 3 min.

[0017] In step (5), the atomic layer deposition temperature is 100 ~ 300 ℃. The deposition material is Pt, a material with a high refractive index difference to X-rays.

[0018] This invention innovatively proposes a high aspect ratio zone plate based on the HSQ + Pt system and its fabrication method. High-resolution pattern definition is achieved using HSQ photolithography layers, and a high-density Pt working layer is deposited on its sidewalls via atomic layer deposition (ALD), thereby constructing a zone plate that combines fine structural control with high diffraction efficiency. This structure significantly improves mechanical stability and process repeatability while maintaining a 5-30 nm linewidth resolution, breaking through the fabrication bottleneck of traditional metal zone plates. It provides a feasible path for the domestic production of high-performance X-ray focusing devices and possesses significant scientific research and engineering application value.

[0019] Compared with the prior art, the beneficial effects of the present invention are: First, this invention innovatively employs an HSQ and Pt material system based on the existing metal single-layer zone plate process. HSQ, as an inorganic photolithography layer material, has extremely low absorption of hard X-rays, which can significantly reduce background attenuation; while Pt has a high atomic number and refractive index, making it an ideal X-ray diffraction material. By depositing Pt on the HSQ template using atomic layer deposition (ALD), a high-density, uniform, and controllable thickness structure can be achieved at the nanoscale, thereby simultaneously obtaining high resolution and high diffraction efficiency.

[0020] Second, this invention employs electron beam lithography to directly define Fresnel zone sheet structures within the HSQ lithographic layer. Electron beam lithography offers extremely high spatial resolution and morphology control precision, achieving linewidths as small as 5 nm while ensuring steep edge sharpness and periodic consistency. This process can be performed on a standard electron beam exposure system, offering high flexibility and repeatability, and providing an ideal template for subsequent atomic layer deposition.

[0021] Third, this invention employs atomic layer deposition (ALD) technology to deposit a Pt working layer on the sidewall region of the HSQ template, resulting in a highly dense, uniformly thick, and low-surface-roughness deposited layer. Compared to traditional electroplating methods, the ALD deposition process eliminates stress accumulation and current distribution effects, making it suitable for forming high-depth, ultra-high aspect ratio diffraction structures. This method can precisely control the Pt layer thickness, achieving stable 1:30~1:60 high aspect ratio structures, significantly improving the mechanical stability and focusing efficiency of the zone plate.

[0022] The high aspect ratio Fresnel zone plate fabricated in this invention enables highly efficient wavefront manipulation of hard X-rays. Theoretical calculations show that this structure achieves a diffraction efficiency of 7-12% in the 1-12 keV band, while exhibiting excellent morphological stability and repeatability. Microscopic imaging verification at 30 nm resolution (diffraction efficiency 10.11%) and 20 nm resolution (diffraction efficiency 8.07%) under 7.2 keV hard X-rays has been achieved. Its fabrication process is stable, compatible, and has a short cycle time, making it suitable for various applications such as hard X-ray microscopy, coherent diffraction imaging, and spectral focusing. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the fabrication process of the high-resolution X-ray Fresnel zone sheet based on Pt-HSQ according to the present invention.

[0024] Figure 2 Scanning electron microscope (SEM) image of the actual fabrication of the Pt / HSQ high-resolution X-ray Fresnel zone lens prepared for this invention.

[0025] Figure 3Scanning electron microscope (SEM) image of the actual fabrication of the 10 nm feature size X-ray Fresnel zone plate lens (template before atomic layer deposition) of the Pt / HSQ system prepared for this invention.

[0026] Figure 4 Scanning electron microscope (SEM) image of the actual fabrication of the 10 nm feature size X-ray Fresnel zone plate lens (after atomic layer deposition) of the Pt / HSQ system prepared for this invention.

[0027] Figure 5 These are X-ray Fresnel zone plate lens imaging test images of the Pt / HSQ system of this invention at a resolution of 20 nm. (a) is the intensity image of the test card; (b) is the phase image of the test card; (c) is the intensity reconstruction result of the focused focal spot; and (d) is the phase reconstruction result of the focused focal spot.

[0028] Figure 6 These are X-ray Fresnel zone plate lens imaging test images of the Pt / HSQ system of this invention at a resolution of 30 nm. (a) is the intensity image of the test card; (b) is the phase image of the test card; (c) is the intensity reconstruction result of the focused focal spot; and (d) is the phase reconstruction result of the focused focal spot. Detailed Implementation

[0029] The present invention will be further described below with reference to the embodiments and accompanying drawings. However, the present invention is not limited to the embodiments. Any simple changes to the process parameters in the embodiments fall within the protection scope of the present invention.

[0030] Example 1: Fabrication of a 20 nm feature size Pt / HSQ system high-resolution X-ray Fresnel zone plate lens with an aspect ratio of 25:1 for 5 keV hard X-ray imaging. The specific steps are as follows: (1) Select a silicon wafer with a silicon nitride window, the thickness of which is 100 nm and the size of which is 2 × 2 mm; (2) A 500 nm thick HSQ electron beam photoresist was spin-coated onto the substrate and baked in a 240 ℃ oven for 2 min to harden it. The result is as follows: Figure 1 As shown in .1; (3) The sample was exposed under an electron beam lithography machine. The exposure pattern was a Fresnel zone lens with a resolution of 20 nm and a diameter of 100 μm. The basic exposure dose was 2000 µC / cm. 2, The proximity effect was corrected for the dose ratio, and the corrected dose ratio ranged from 0.5 to 1.5. The results are as follows: Figure 1 As shown in Figure 2. After exposure, the solution was developed in a 1:3 TMAH / H2O mixed solution at 50 °C for 2 min, followed by fixing in H2O for 30 s. The results are shown in Figure 2. Figure 1 As shown in .3; (4) Atomic layer deposition was performed on the sample. The deposited metal was Pt, the deposition temperature was 280 ℃, and the deposition thickness was 20 nm. The results are as follows: Figure 1 As shown in Figure 4, the final sample's actual processing scanning electron microscope image is as follows: Figure 2 As shown. Figure 2 (In the image above, sub-image af shows scanning electron microscope images of different regions of the sample at different magnifications.) Figure 5 The imaging test results are for the 20 nm feature size X-ray Fresnel zone lens prepared in this embodiment. Figure 6 The results are from X-ray Fresnel zone plate lens imaging tests with a feature size of 30 nm.

[0031] Example 2: Fabrication of a 10 nm resolution Pt / HSQ system high-resolution X-ray Fresnel zone plate lens with an aspect ratio of 35:1 for 5 keV hard X-ray imaging. The specific steps are as follows: (1) Select a silicon wafer with a silicon nitride window, the thickness of which is 100 nm and the size of which is 2 × 2 mm; (2) A 350 nm thick HSQ electron beam photoresist was spin-coated onto the substrate and baked in an oven at 240 °C for 2 min to harden it. The result is as follows: Figure 1 As shown in .1; (3) The sample was exposed under an electron beam lithography machine. The exposure pattern was a grating line with a linewidth of 10 nm and a period of 40 nm. The exposure dose was 2000 µC / cm. 2, The proximity effect was corrected for the dose ratio, and the corrected dose ratio ranged from 0.5 to 1.5. The results are as follows: Figure 1 As shown in Figure 2, the actual fabrication scanning electron microscope image is as follows: Figure 3 As shown ( Figure 3 In the image, sub-image ai represents scanning electron microscope (SEM) images of different regions of the sample at different magnifications.

[0032] After exposure, the solution was developed in a 1:3 TMAH / H2O mixed solution at 50 °C for 2 min, followed by fixing in H2O for 30 s. The results are as follows. Figure 1 As shown in .3; (4) Atomic layer deposition was performed on the sample. The deposited metal was Pt, the deposition temperature was 280 ℃, and the deposition thickness was 10 nm. The results are as follows: Figure 1 As shown in Figure 4, the final sample's actual processed scanning electron microscope cross-sectional image is as follows. Figure 4 As shown. Figure 4 In the image, sub-image ai represents scanning electron microscope (SEM) images of different regions of the sample at different magnifications.

Claims

1. A high-resolution X-ray Fresnel zone plate based on Pt-HSQ, characterized in that, Using the Pt-HSQ metal-inorganic material system, a diffraction structure with a large aspect ratio and quasi-periodic dense stripes of Pt material, which is required for X-ray zone plate lenses, is formed through electron beam lithography and ALD processes. This enables diffraction focusing and imaging with magnification from soft X-ray to hard X-ray bands. Its structure, from bottom to top, consists of: a silicon substrate, a diaphragm window, a photolithography template, and a working structure layer covering the template; the working structure layer is obtained by etching a pattern on the photolithography layer and then depositing high-density material using an atomic layer deposition process. The photolithography layer material is Si-containing HSQ, with a template linewidth of 5-50 nm and a period of 20-200 nm; wherein the template thickness is positively correlated with the linewidth, and the thickness ranges from 350 nm to 2000 nm. The working layer is grown by atomic layer deposition, using the noble metal Pt as the material; the working layer thickness is 1 ~ 100 nm. Fresnel zone plates are positioned above the diaphragm window, with their working direction perpendicular to the window plane, enabling diffraction modulation of incident X-rays, including focusing, dispersion, or interference modulation; the device has a linewidth as small as 20 nm and a height exceeding 500 nm, achieving high-efficiency X-ray wavefront modulation under high-resolution conditions.

2. The high-resolution X-ray Fresnel zone plate according to claim 1, characterized in that, The diaphragm window is square, with a thickness of 100 ~ 500 nm and a side length of 1 ~ 5 mm.

3. The high-resolution X-ray Fresnel zone plate according to claim 2, characterized in that, The diaphragm window material is silicon nitride, silicon dioxide, or silicon.

4. The high-resolution X-ray Fresnel zone plate according to claim 3, characterized in that, Imaging at 30 nm and 20 nm resolutions was achieved under 7.2 keV hard X-rays. The theoretical focusing efficiency for 30 nm resolution was 13.46%, and the measured focusing efficiency was 10.11%. The theoretical focusing efficiency for 20 nm resolution was 13.13%, and the measured focusing efficiency was 8.07%. For a Fresnel zone plate lens with a feature size of 10 nm, the theoretical focusing efficiency was 3.36%, and the measured focusing efficiency was 1.78%.

5. The method for preparing a high-resolution X-ray Fresnel zone sheet as described in any one of claims 1-4, characterized in that, The specific steps are as follows: (1) Thin film windows were prepared on a silicon substrate using PECVD; (2) A photolithography layer HSQ template is formed on the thin film window; (3) The pattern of the diffraction structure is formed in the photolithography layer using electron beam lithography; (4) Develop the sample obtained in step (3) to obtain the template structure; (5) Atomic layer deposition of Pt is performed on the sample obtained in step (4) to grow a high depth working layer of the diffraction structure in the sidewall region of the template, thereby forming a diffraction-type micro-nano optical structure with a large aspect ratio.

6. The preparation method according to claim 5, characterized in that: In step (1), the thin film window is square, with a thickness of 100 ~ 500 nm and a side length of 1 ~ 5 mm; In step (2), the photolithography layer thickness is 50 ~ 4000 nm, and it is baked to harden. The baking temperature is 150 ~ 180 ℃ and the time is 1 ~ 30 min. In step (3), the exposure base dose of the electron beam lithography is 500 ~ 8000 μC / cm², the exposure relative dose is 0.05 ~ 2, the development temperature is 40 ~ 50 ℃, and the development time is 1 ~ 3 min; In step (5), the atomic layer deposition temperature is 100 ~ 300 ℃.

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