A metastable helium atom holographic lithography device, imaging method and application

Abstract

The application provides a metastable helium atom holographic lithography device and an imaging method and application, which comprises a ground state helium beam generating assembly, an electron excitation gun, a collimating diaphragm and a holographic mask along a transmission path of a helium atom beam, the holographic mask comprises a holographic mask layer and a supporting layer, the thickness of the supporting layer controls the working distance between the holographic mask layer and a lithography sample, and a through hole is arranged at a position corresponding to an imaging area; the holographic mask layer has a preset pattern composed of a nano-pore array, the holographic diffraction intensity distribution of the metastable helium atom beam is formed on the surface of the lithography sample by modulating the amplitude and phase of the metastable helium atom beam, and the patterning etching with a sub-nanometer resolution is realized. The application can realize high-precision and high-flexibility holographic lithography with a short imaging distance, significantly improves the lithography efficiency and practicability, and has a limit resolution superior to that of traditional EUV lithography.

Description

Technical Field

[0001] This invention belongs to the field of atomic lithography equipment technology, and in particular to a metastable helium atom holographic lithography device, imaging method and application for semiconductor manufacturing. Background Technology

[0002] Photolithography, a key process in integrated circuit manufacturing, is based on photochemical reactions. It precisely transfers fine images from a mask to the surface of a substrate (wafer), making it a core step in semiconductor device manufacturing. With the continuous iteration of integrated circuit manufacturing technology, the light source in lithography machines has evolved from ultraviolet (UV) to deep ultraviolet (DUV) and extreme ultraviolet (EUV). Currently, deep ultraviolet lithography machines are mainly equipped with a 193 nm wavelength light source, supporting the manufacturing needs of process nodes below 90 nm. Meanwhile, extreme ultraviolet lithography machines (EUV) use a 13.5 nm wavelength light source, becoming a key technological support for advanced processes at 7 nm and below, greatly promoting the development of semiconductor manufacturing processes towards high-density integration.

[0003] However, as process nodes continue to advance to smaller scales, existing lithography technology systems have exposed many bottlenecks: on the one hand, limited by optical principles, the resolution of lithography machines is difficult to further improve, making it difficult to meet the transfer needs of smaller patterns in the future; on the other hand, equipment costs are increasing exponentially, and system complexity is increasing significantly, posing a huge challenge to chip manufacturing companies. Therefore, exploring new light sources and lithography technologies with higher resolution, lower manufacturing costs, and greater development potential has become a hot research direction in the global semiconductor manufacturing field.

[0004] Against this backdrop, atomic lithography, with its extremely short wavelengths (e.g., the wavelength of a helium atom at 100K is only 0.1 nm), is considered a strong candidate for next-generation lithography. The core idea of ​​atomic lithography is to generate patterns using the interaction between metastable atomic beams and photoresist (usually a self-assembled monolayer). Specifically, when metastable atoms bombard the photoresist, a de-excitation process occurs, releasing energy and causing the molecular bonds in the photoresist to break, altering its etching resistance. Combined with wet etching processes, the patterns formed by metastable atoms on the photoresist can be precisely transferred to the substrate surface.

[0005] In 1995, Berggren's research team at Harvard University pioneered a breakthrough in proximity exposure technology for metastable atoms. They successfully transferred the grid structure of a copper mesh onto a thiol-based photoresist by directly irradiating metastable argon atoms onto a copper mesh used in a transmission electron microscope (TEM). Since then, numerous research teams have continued to delve into this field, successively achieving proximity exposure of metastable atoms on photoresist, obtaining pattern sizes smaller than 50 nm and edge resolutions of less than 20 nm.

[0006] However, atomic lithography technology also faces key obstacles in its development. Since atomic beams cannot penetrate solid materials, the atomic lithography mask must be designed with a porous structure to ensure the smooth passage of the atomic beam. However, this structure directly prevents proximity lithography from generating closed-path patterns. To overcome this challenge, Fujita et al. at NEC's Basic Research Laboratory in Japan innovatively introduced binary computational holography based on Fraunhofer diffraction, designed an atomic holographic mask, and successfully fabricated the holographic mask by finely etching SiN thin films using electron beam lithography. Experimental results strongly demonstrate that a laser-cooled metastable neon atomic beam can clearly form a target image on a microchannel plate (MCP) after passing through the holographic mask. However, this technology has significant limitations: Fraunhofer diffraction-based atomic holography experiments require the distance between the target pattern and the mask to meet the far-field limit. Without the introduction of atomic lenses, this technology cannot be used to create target patterns with high spatial resolution. However, there is currently no atomic lens technology in the industry that can achieve nanometer-level precision pattern generation.

[0007] US006165688A discloses a method for fabricating microstructures on a substrate by inducing passivation layer desorption through metastable atomic bombardment. The principle is as follows: a beam of metastable atoms (such as argon atoms) is directly irradiated onto a substrate covered with a passivation layer (such as a hydrogen passivation layer). The bombardment of metastable atoms causes localized desorption of the passivation layer, exposing the substrate surface. Microstructures are then formed in the exposed area using conventional processes (such as etching or chemical reactions). This method utilizes the de-excitation energy of metastable atoms (e.g., 11.7 eV for argon atoms) to remove the passivation layer, achieving high resolution (the edge resolution of the pattern shown in the experiment is approximately 20 nm), and avoiding resolution loss due to charged particle scattering. However, this method is a proximity exposure method, limited by the requirement that the mask must have an open structure, making it impossible to generate closed-path patterns and resulting in poor flexibility. WO 2015 / 011457 A1 describes a method for forming patterns on a substrate using an atomic or molecular beam (preferably a metastable helium atom beam) through a mask. The mask uses a porous material (such as a quartz film or graphene) as a substrate, forming the desired pattern (e.g., a Fourier transform pattern of the target image) by filling some of the pores, and operates under Fraunhofer far-field diffraction conditions. After the atomic beam passes through the mask, a diffraction image based on the mask pattern is formed on the substrate, and the resolution can be adjusted using atomic lenses or focusing lenses. However, the far-field diffraction used in this method results in a large distance between the mask and the substrate, making it impossible to generate holographic patterns with nanometer-level resolution on the substrate, and the need for focusing with atomic lenses increases the complexity of the equipment.

[0008] Therefore, there is an urgent need in the field for a metastable atomic holographic lithography device that can maintain good flexibility and achieve nanoscale resolution targets without relying on atomic lenses, so as to promote semiconductor manufacturing processes to a higher level and meet the process node requirements of future integrated circuits that continue to shrink. Summary of the Invention

[0009] The purpose of this invention is to solve the problems of poor resolution and insufficient flexibility of existing atomic holographic lithography devices, and to provide a metastable helium atom holographic lithography device, its imaging method, and its applications that can realize nanoscale processes.

[0010] The technical concept of this invention is to first generate a quasi-monochromatic ground-state helium atom beam based on adiabatic expansion, then use an electron excitation gun to excite the ground-state helium atoms into metastable helium atoms, then use a collimating aperture to enhance the lateral coherence of the metastable helium atom beam, and use a binary holographic mask based on near-field Fresnel diffraction to perform high-precision modulation of the amplitude and phase of the metastable helium atoms, and finally use wet etching to transfer the holographic imaging pattern to the substrate, thereby generating arbitrary target nanopatterns with feature size less than 10 nm.

[0011] The "near-field Fresnel diffraction" mentioned in this invention is an innovative solution proposed by scientists to address the insufficient resolution of far-field holographic imaging. Torstein Nesse of the Norwegian University of Science and Technology has conducted in-depth research on binary holography based on near-field Fresnel diffraction. This technique significantly shortens the distance between the mask and the imaging plane, theoretically possessing the potential to generate nanometer-resolution images. However, binary holography mainly relies on first-order diffraction effects to achieve phase encoding, which often results in the generation of multi-order diffraction images, i.e., unnecessary redundant images. To address this problem, Peng Renjun of the University of Electronic Science and Technology of China proposed a novel binary computational holography method. This method can construct a holographic mask field through the superposition of Fresnel basis functions, generating a binary holographic mask without relying on phase encoding. Computational simulation results show that a coherent atomic beam passing through this mask can produce a single real image, effectively avoiding interference from redundant images.

[0012] This invention creatively applies near-field Fresnel diffraction technology to a metastable helium atom holographic lithography device, solving the problems of traditional atomic lithography's inability to generate closed path patterns in close-range exposure and insufficient resolution in far-field holographic imaging, and providing a potential technical solution for next-generation integrated circuit manufacturing.

[0013] In a first aspect, the present invention provides a metastable helium atom holographic lithography apparatus, comprising, along the propagation path of the helium beam:

[0014] (a) A ground-state helium beam generating assembly, comprising a helium source supply container and a temperature regulation module, the temperature regulation module being used to regulate the wavelength of the helium beam by controlling the temperature of the helium beam to provide a quasi-monochromatic ground-state helium atom beam;

[0015] (b) An electron excitation gun configured to excite ground-state helium atoms into metastable helium atoms by electron beam collision;

[0016] (c) Collimation stop, used to improve the lateral coherence of metastable helium atom beam;

[0017] (d) A holographic mask, comprising a holographic mask layer and a support layer stacked together, wherein:

[0018] The upper surface of the support layer is in contact with the holographic mask layer, and the lower surface is in contact with the photolithography sample. Its thickness is designed to adjust the working distance between the holographic mask layer and the photolithography sample. A through hole is provided at the position corresponding to the imaging area of ​​the holographic mask layer to allow the helium beam to pass through.

[0019] The imaging region of the holographic mask layer has a preset pattern composed of a nanopore array. The nanopore array forms a holographic diffraction intensity distribution of metastable helium atoms on the surface of the photolithographic sample by modulating the amplitude and phase of the metastable helium atom beam, thereby achieving patterned etching with nanometer-level resolution.

[0020] According to the holographic lithography apparatus provided by the present invention, the ground-state helium atom beam generating component includes a helium source supply container and a temperature regulation module. The helium source supply container is a sealed container for containing high-pressure helium gas (preferably 10-100 bar), and it has a micrometer-sized (preferably 5-30 μm in diameter) through-hole (helium gas nozzle). There is one micrometer-sized through-hole. The helium source supply container can also be fluidly connected to a helium gas conduit for supplying helium gas. When the micrometer-sized through-hole (helium gas nozzle) is placed in a high vacuum environment (preferably with a pressure not exceeding 10 bar), the temperature regulation module can be used to supply helium gas. -5 At a pressure of mbar, due to the extreme pressure difference across the through-hole, the helium gas inside the container is ejected through quasi-steady-state adiabatic expansion, generating a directional helium beam. The beam velocity V satisfies: , where K b Where λ is Boltzmann constant, m is the mass of helium gas, and T0 is the temperature of the beam. Based on the de Broglie wavelength formula λ = h / (mν) (where h is Planck constant), it can be seen that the wavelength of the helium atom beam can be controlled by adjusting T0.

[0021] The temperature regulation module includes a heating element and a cooling element disposed on the outer wall of the helium source supply container, used to regulate the helium beam temperature to achieve adjustment of the helium beam wavelength. In some embodiments of the present invention, the heating element is a resistance heating wire, and the cooling element is a copper braided strip.

[0022] In a preferred embodiment of the present invention, the ground-state helium beam generating component is configured to provide a quasi-monochromatic ground-state helium atom beam with a wavelength of 0.05-0.22 nm, preferably 0.09-0.11 nm.

[0023] In an exemplary embodiment of the holographic lithography apparatus provided by the present invention, the electron excitation gun may include:

[0024] Heating the filament to release electrons;

[0025] A spherical cathode, grid, and anode are used to generate a radial electric field;

[0026] Focusing solenoids and deflecting electrodes are used to focus and deflect electron beams.

[0027] Preferably, the voltage of the spherical cathode can be between 0 and 200V, and more preferably 20-30V. This is because, according to existing measurements based on the present invention, a strong metastable helium atom beam can be generated when the cathode voltage is equal to 21.6V. As the voltage further increases, collisions between electrons and helium atoms produce forward and backward scattering, respectively increasing and decreasing the wavelength of the metastable helium atoms, thus affecting the monochromaticity of the helium beam.

[0028] According to the holographic lithography apparatus provided by the present invention, the collimating aperture can be a micrometer-scale slit aperture or a sub-millimeter-scale circular aperture. Since the divergence angle of the free jet beam generated by adiabatic expansion combined with electron excitation is relatively large, the collimating aperture is used to collimate the beam, giving it sufficient spatial coherence to achieve atomic holographic imaging. The slit aperture has a microchannel with an aspect ratio ≤ 2:1, and the divergence angle is compressed using geometric constraints; the circular aperture is designed based on the van Sitter-Zehnderik theorem, and its aperture radius ρ satisfies L... c =Rλ / ρ coherence length modulation relationship (L c (where λ is the transverse coherence length and λ is the average wavelength of the atomic beam).

[0029] In a preferred embodiment of the present invention, by selecting a combination of aperture parameters ρ=100-300 μm and propagation distance R=0.3-0.5 m, a collimated atomic beam with lateral coherence ≥1 μm and divergence angle ≤0.3 mrad is finally output, which meets the spatial coherence requirements of atomic holographic imaging.

[0030] According to the holographic lithography apparatus provided by the present invention, the holographic mask includes a holographic mask layer and a support layer. The support layer is made of a material with a low coefficient of thermal expansion and inertness to metastable helium atoms, such as silicon, borosilicate glass, AlN ceramic, nickel-based alloys, etc. In some embodiments of the present invention, the holographic mask layer is made of a silicon nitride thin film, on which a nanoscale array of micropores for modulating the amplitude and phase of metastable helium atoms is formed.

[0031] In an exemplary embodiment of the present invention, the method for fabricating the holographic mask layer may include computer generation of the holographic mask and microfabrication of the mask.

[0032] The design principle of the holographic mask is as follows: assuming the intensity distribution of the target image is... The field distribution of atoms at the mask is deduced by inverse Fresnel transformation. . It is a complex matrix, encoded using a 4×4 binary matrix. The amplitude and phase of each matrix element represent the mask field as a binary matrix composed of 0s and 1s. In actual manufacturing, the positions with values ​​of 1 are etched as through holes to create a holographic mask. This holographic technique can be used to form arbitrary patterns, and the resolution depends on parameters such as the atomic beam wavelength, the distance between the mask layer and the photolithographic sample, and the size of the mask openings.

[0033] The microfabrication of the holographic mask layer can be performed through the following steps: spin-coating photoresist on a silicon nitride thin film, patterning the photoresist by electron beam lithography, and then transferring the nanopore array pattern onto the silicon nitride thin film by reactive ion etching to obtain the holographic mask layer.

[0034] In some embodiments of the present invention, the photoresist used for the microfabrication of the holographic mask layer is polymethyl methacrylate (PMMA). The silicon nitride thin film is typically written as SiN. x In this equation, X represents the atomic ratio of nitrogen (N) to silicon (Si). The stoichiometric compound of silicon nitride is Si3N4, where x = 4 / 3, approximately 1.33. However, in practical applications, due to factors such as the fabrication process, the composition of the silicon nitride film may deviate from the stoichiometric ratio, and the value of x will vary within a certain range, typically fluctuating between 0 and 1.33.

[0035] In a preferred embodiment of the present invention, the metastable helium atom holographic lithography apparatus further includes a conical aperture disposed between the ground-state helium beam generating component and the electron excitation gun along the transmission path of the helium beam. The conical aperture is used to compress the divergence angle of the helium beam through geometric constraints.

[0036] In various embodiments of the present invention, the metastable helium atom holographic lithography apparatus further includes a vacuum chamber, in which the ground-state helium atom beam generating component, electron excitation gun, collimating aperture, and holographic mask are all disposed. The vacuum chamber maintains a specific vacuum level to reduce collisions between metastable helium atoms and other gas molecules, ensuring the lifetime of the metastable helium atoms and the stability of the lithography process. Preferably, the metastable helium atom holographic lithography apparatus of the present invention is also equipped with a beam monitoring and control system for real-time monitoring of parameters of the metastable helium atom beam, such as intensity, energy distribution, and coherence, and for real-time control of components such as the ground-state helium atom beam generating component, electron excitation gun, and collimating aperture based on the monitoring results, to ensure the accuracy and consistency of the lithography process.

[0037] The advantages of the metastable helium atom holographic lithography device provided by the present invention are: (1) It can generate arbitrary patterns, which makes up for the shortcomings of metastable atom proximity exposure which cannot form closed path patterns; (2) It adopts Fresnel diffraction near-field holographic lithography method, which can image without atomic lenses, greatly shortening the distance between the mask and the photoresist; (3) The limit resolution of the generated pattern can reach the nanometer level, which is better than the limit resolution of the most advanced EUV lithography single exposure in the industry.

[0038] Secondly, the present invention provides an atomic near-field holographic imaging method, which includes the following steps using the metastable helium atom holographic lithography apparatus provided in the first aspect of the present invention:

[0039] (1) Provide photolithography sample: Coat the substrate surface with a self-assembled monolayer photoresist that is sensitive to metastable helium atoms to provide a photolithography sample;

[0040] (2) The helium gas in the helium source supply container is injected to generate a directional helium beam. The temperature adjustment module is used to adjust the wavelength of the helium beam to 0.05-0.22nm by controlling the temperature of the helium beam, so as to provide a quasi-monochromatic ground state helium atom beam.

[0041] (3) The ground-state helium atom is excited into a metastable helium atom using the electron excitation gun described above;

[0042] (4) The collimation aperture is used to collimate the metastable helium atom beam to improve the transverse coherence of the metastable helium atom beam;

[0043] (5) The collimated metastable helium atom beam is coherently irradiated on the holographic mask and holographically imaged on the self-assembled monolayer photoresist after passing through the nanopore array of the holographic mask layer, forming an exposure area with nanoscale resolution.

[0044] (6) The exposed pattern is transferred to the substrate by wet etching to generate the target nanopattern.

[0045] According to the holographic imaging method provided by the present invention, the wet etching involves placing a photolithographic sample containing a self-assembled monolayer photoresist (SAM photoresist) and a substrate after exposure to metastable helium atoms into a chemical reagent for etching, so as to form a predetermined pattern on the substrate.

[0046] The SAM photoresist is a photoresist system based on self-assembled monolayers (SAM) technology. It forms a highly ordered monolayer structure on the substrate surface through spontaneous intermolecular interactions (such as chemical bonds and van der Waals forces), achieving nanoscale patterning by utilizing molecular self-assembly properties. Its functional molecules can be selected from organic molecules containing groups such as thiols (-SH) and silanes (-Si(OR)3), which can form chemical bonds or strong adsorption with the substrate (such as gold or silicon). For example, thiols form SAM on gold surfaces, and silanes form SAM on silicon surfaces. In some embodiments of the present invention, the substrate is silicon or gold, and the SAM photoresist is an organic molecule containing thiols or silane groups, such as dodecylthiol (forming a SAM thickness of approximately 1.3-1.8 nm), octadecyltrichlorosilane (forming a SAM thickness of approximately 2.2-2.7 nm), dodecyltrichlorosilane (forming a SAM thickness of approximately 2.1 nm), butylthiol, octylthiol, and heptylthiol.

[0047] Taking a straight-chain alkathiol molecule as an example, its thiol group is bonded to the substrate, while the hydrocarbon chain composed of CH bonds is arranged regularly outwards, forming a hydrophobic, nonpolar surface environment. When metastable helium atoms are incident on the surface of the alkathiol monolayer molecule, the metastable helium atoms undergo Penning de-excitation, releasing electrons and causing the molecular bonds of the alkathiol molecule to break. Generally, when the metastable helium beam dose is relatively low, the alkathiol molecule usually experiences CH or CS bond breakage, subsequently reacting with oxygen and water molecules in the air to form hydrophilic polar groups or causing the molecule to detach from the substrate. Both of these situations will make the monolayer molecules in the exposed area hydrophilic and thus be wet-etched away, leading to the chemical etching of the substrate in the exposed area to form a predetermined pattern. At this time, the alkathiol monolayer molecule exhibits a positive gel appearance. If the metastable helium atom dose exceeds a certain threshold, the C / C bonds of the alkathiol molecule will break, resulting in a cross-linking reaction to form a three-dimensional network structure. This results in a denser molecular structure in the exposed areas compared to the unexposed areas, allowing it to be preserved during wet etching. The unexposed monolayer and the underlying substrate are etched away, at which point the alkylthiol monolayer exhibits a negative resist state. The average molecular density of alkylthiols is approximately 5 × 10⁻⁶. 14 cm -2 Therefore, the average area occupied by each molecule is only 0.2 nm. 2 Furthermore, metastable helium atoms (2 3 The excitation internal energy of S is 19.8 eV. Within this energy range, the mean free path of secondary electrons in a monolayer is less than 1 nm. Therefore, the interaction region of metastable atoms with a single molecule should be limited to a radius of a few angstroms. So theoretically, this material can produce a nm-level limiting resolution.

[0048] The method of this invention combines the functions of generating a quasi-monochromatic ground-state helium atom beam based on adiabatic expansion, exciting ground-state helium atoms into metastable helium atoms with an electron excitation gun, improving the lateral coherence of the metastable helium atom beam with a collimating aperture, high-precision modulation of the amplitude and phase of metastable helium atoms by a holographic mask, and transferring holographic imaging patterns to a substrate by wet etching. It can form an exposure area with nanoscale resolution on the photoresist, and then accurately form the target nanoscale pattern on the substrate through chemical etching.

[0049] A third aspect of the present invention provides the application of the metastable helium atom holographic lithography apparatus of the first aspect and the atomic near-field holographic imaging method of the second aspect in semiconductor chip manufacturing.

[0050] The application utilizes the low energy and short wavelength characteristics of metastable helium atoms to overcome the diffraction limit of traditional optical lithography and achieve nanoscale linewidths. Combined with the molecular self-assembly properties of SAM photoresists (such as octadecyltrichlorosilane SAM), defect-free nanotemplates can be formed to guide precise patterning.

[0051] Compared to existing technologies, this invention overcomes the shortcomings of traditional atomic lithography, such as the inability to generate closed-path patterns through near-field exposure and insufficient resolution in far-field holographic imaging. It achieves the generation of nanoscale holographic exposure regions on photoresist through near-field Fresnel diffraction without the need for atomic lenses, and then transfers the image to the substrate via chemical wet etching. This invention achieves high precision (nanometer-level resolution, with a limit below 10nm), high flexibility (capable of generating arbitrary patterns, including closed-path patterns), and a short imaging distance (the distance between the mask and photoresist is only the substrate thickness, enabling near-field imaging), significantly improving lithography efficiency and practicality, with a limiting resolution superior to traditional EUV lithography. Attached Figure Description

[0052] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0053] Figure 1 This is a schematic diagram of the metastable helium atom holographic lithography device provided by the present invention.

[0054] Figure 2 This is a schematic diagram of the ground-state helium atom beam generating component used in the metastable helium atom holographic lithography apparatus provided by the present invention.

[0055] Figure 3 This is a schematic diagram of the electron excitation gun used in the metastable helium atom holographic lithography apparatus provided by the present invention.

[0056] Figure 4 This is a schematic diagram of the slit aperture and circular aperture used in the metastable helium atom holographic lithography apparatus provided by the present invention.

[0057] Figure 5A is a schematic diagram of the holographic mask used in an embodiment of the present invention.

[0058] Figure 5B is a schematic diagram of the holographic mask / SAM photoresist / substrate stack used in the embodiment of the present invention.

[0059] Figure 6 This is a schematic diagram of exposure using the holographic mask / SAM photoresist / substrate stack shown in Figure 5B. Detailed Implementation

[0060] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0061] Figure 1 This is a schematic diagram of the metastable helium atom holographic lithography device used in this embodiment of the invention, which includes: a helium nozzle 1, a cone-shaped body 2, an electron excitation gun 3, a collimating aperture 4, a holographic mask 5, a lithography sample 6, an electron gun filament current source 7, and an electron gun high-voltage pulse generator 8.

[0062] The metastable helium atom holographic lithography device provided by the present invention comprises the following components: (1) a ground-state helium atom beam generation system, mainly composed of a helium gas conduit, a cooling copper braided strip, a resistance heating wire, a high-pressure helium gas container, a micron-sized through-hole, and a conical body (see...). Figure 2 (2) The electron excitation gun mainly consists of a heating filament, electron emission material, spherical cathode, grid, anode, focusing solenoid and deflection electrode (see Figure 3 (3) Collimation stop, selected from one of a micrometer-scale slit and a circular stop (see Figure 4 (4) Holographic mask (see Figure 5, Figures A and B).

[0063] The method for near-field holographic imaging of atoms using the metastable helium atom holographic lithography device provided by the present invention includes: (1) generating a quasi-monochromatic ground-state helium atom beam using a ground-state helium atom beam generation system; (2) exciting the quasi-monochromatic ground-state helium atom beam to a metastable state using an electron excitation gun (2 3 (3) The metastable helium atom beam coherently irradiates the holographic mask after passing through the collimating aperture; (4) The metastable helium atoms are holographically imaged on the photoresist through the mask to form the exposure area of ​​the nanoscale pattern; (5) The exposed substrate and SAM photoresist are placed in a chemical reagent for wet etching. The SAM photoresist in the exposed area protects the substrate below from being etched, while the SAM photoresist in the unexposed area, along with a certain thickness of substrate below it, is etched away, thereby transferring the nanoscale target pattern to the substrate surface.

[0064] Example

[0065] The metastable helium atom holographic lithography apparatus provided by this invention is used for near-field atomic holographic imaging. The working process is as follows:

[0066] (1) such as Figure 2 As shown, high-pressure helium gas (typically 20-80 bar) is introduced into a high-pressure helium container through a helium gas conduit. A micrometer-sized orifice (e.g., 20 μm) is opened at one end of the container to allow fluid communication between the inside and outside of the container. The outside of the container is in a high-vacuum environment (e.g., 10...). -5 Therefore, a huge pressure difference (e.g., about 10 mbar) is created between the inside and outside of the container. 8 (mbar), thus causing the helium gas in the container to be ejected through the small hole in the form of adiabatic expansion. Almost all the hysteresis of the atoms in the high-pressure container is converted into kinetic energy of longitudinal motion, so the velocity of the helium beam can be expressed as:

[0067]

[0068] T0 represents the beam temperature, meaning the velocity (wavelength) of the helium beam depends on the temperature of the beam source. The wavelength of the helium beam can be adjusted by jointly cooling the copper woven bag and the resistance heating wire to regulate the temperature of the beam source.

[0069] (2) The quasi-monochromatic helium beam will be excited to a metastable state after passing through the electron excitation gun (2 3 S). For example Figure 3 As shown, the electron gun for exciting helium atoms consists of a spherical cathode, a grid, a grounded anode, a solenoid, and deflection electrodes. During operation, the spherical cathode, which is subjected to a negative voltage by a high-voltage pulse generator, releases electrons under heating by a filament current source. The anode is grounded, and a radial electric field is generated inside the electron gun, causing the electrons released from the cathode to converge at the center of the sphere. Then, under the constraint of a horizontal magnetic field generated by the solenoid, the electrons are focused into an electron beam parallel to the helium atom beam, colliding with the helium beam and exciting it to a metastable state. In actual operation, a certain voltage is applied to the deflection electrodes to deflect the electrons in the beam and the helium ions generated by ionization out of their propagation path, preventing them from incident on the holographic mask. According to existing laboratory measurements, a cathode voltage of 21.6V can produce a relatively strong metastable helium atom beam. As the voltage further increases, the collisions between electrons and helium atoms produce forward and backward scattering, increasing and decreasing the wavelength of the metastable helium atoms, respectively, affecting the monochromaticity of the helium beam.

[0070] (3) The divergence angle of the free jet beam generated by adiabatic expansion combined with electronic excitation is relatively large. Therefore, beam collimation is required to ensure sufficient spatial coherence for atomic holographic imaging. Beam collimation can be achieved by placing slits or apertures (such as...) in the helium beam propagation path. Figure 4(As shown) to achieve this. According to the van Sitzernik theorem, when an incoherent metastable helium atom beam with an average wavelength of λ propagates a distance R through a small aperture with a radius of ρ, a coherent region with a scale of Rλ / ρ (lateral coherence length) can be formed on the holographic mask.

[0071] (4) Coherent metastable helium atoms are holographically imaged on SAM photoresist after passing through the holographic mask, forming a nanoscale exposure pattern. The image contrast and intensity of Fresnel near-field holographic imaging are closely related to the distance between the mask and the photoresist. In the embodiments of the present invention (as shown in Figure 5), the holographic mask is covered with silicon nitride (SiN). x (X=1.33) A silicon wafer with a micron-sized square via in the center, and SiN above the via. x The thin film is etched with an electron beam to form a series of nanoscale pore arrays (the white squares in the figure indicate the locations of the pores). In an embodiment of the present invention, a TEM Grid (transmission electron microscope grid) with a square hole in the center, made of Si, is used as the support layer of the holographic mask, hereinafter referred to as "Si TEM Grid".

[0072] Holographic mask layer (SiN) x The distance between the thin film and the SAM photoresist is equal to that between SiN and SAM. x The thickness of the Si TEM Grid beneath the thin film. Therefore, the thickness of the Si TEM Grid can be set to achieve the optimal thickness for holographic imaging. Atomic holographic mask fabrication technology includes computer generation technology for holographic masks and microfabrication and synthesis technology for masks. The design principles and microfabrication methods of the holographic mask layer are as described above.

[0073] (5) such as Figure 6 As shown, the SAM photoresist after metastable helium atom exposure and the silicon substrate are placed in a chemical reagent for wet etching to transfer the pattern onto the Si substrate. In this embodiment of metastable helium atom lithography, the SAM photoresist used is an octadecyltrichlorosilane self-assembled monolayer material.

[0074] Metastable helium atom beams generated by adiabatic expansion combined with electron excitation (He * After collimation, coherent irradiation is applied to SiN. x On a holographic mask made of thin film, He * Fresnel near-field diffraction is performed through a mask to form an "SF06" type exposure region with a feature size of less than 10 nanometers on a self-assembled monolayer (SAM) (the square pattern is the zero-order diffraction image). When He *After the exposure dose on the SAM exceeds the critical dose, the SAM on the Si substrate is immersed in a chemical reagent for wet etching, finally rinsed with pure water, dried, and then sent to AFM or SEM to scan the surface morphology of the Si substrate. A raised "SF06" pattern is observed on the Si substrate, as shown below. Figure 6 As shown, its lateral feature size is less than 10 nanometers, and its height depends on the etching time.

Claims

1. A metastable helium atom holographic lithography apparatus, comprising, along the propagation path of a helium atom beam: (a) A ground-state helium beam generating assembly, comprising a helium source supply container and a temperature regulation module, the temperature regulation module being used to regulate the wavelength of the helium beam by controlling the temperature of the helium beam to provide a quasi-monochromatic ground-state helium atom beam; (b) An electron excitation gun configured to excite ground-state helium atoms into metastable helium atoms by electron beam collision; (c) Collimation stop, used to improve the lateral coherence of metastable helium atom beam; (d) A holographic mask, comprising a holographic mask layer and a support layer stacked together, wherein: The upper surface of the support layer is in contact with the holographic mask layer, and the lower surface is in contact with the photolithography sample. Its thickness is designed to adjust the working distance between the holographic mask layer and the photolithography sample. A through hole is provided at the position corresponding to the imaging area of ​​the holographic mask layer to allow the helium beam to pass through. The imaging region of the holographic mask layer has a preset pattern composed of a nanopore array. The nanopore array modulates the amplitude and phase of the metastable helium atom beam to form a holographic diffraction intensity distribution of metastable helium atoms on the surface of the photolithographic sample, thereby achieving patterned etching with nanometer-level resolution.

2. The holographic lithography apparatus according to claim 1, wherein, The helium source supply container is a sealed container that contains high-pressure helium gas and has micron-sized through holes to generate a directional helium beam through adiabatic expansion. Preferably, the temperature regulation module includes a heating element and a cooling element disposed on the outer wall of the injection duct. Preferably, the heating element is a resistance heating wire, and the cooling element is a copper braided strip. Preferably, the ground-state helium beam generating component is configured to provide a quasi-monochromatic ground-state helium atom beam with a wavelength of 0.05-0.22 nm, preferably 0.09-0.11 nm.

3. The holographic lithography apparatus according to claim 1, wherein, The electron excitation gun includes: Heating the filament to release electrons; A spherical cathode, grid, and anode are used to generate a radial electric field; Focusing solenoids and deflecting electrodes are used to focus and deflect electron beams. Preferably, the voltage of the spherical cathode is between 0 and 200V, and more preferably 20-30V.

4. The holographic lithography apparatus according to claim 1, wherein, The collimation aperture is a micrometer-level slit aperture or a sub-millimeter-level circular aperture; Preferably, the slit aperture has a microchannel with an aspect ratio ≤ 2:1; the circular aperture is designed based on the Fraunhofer diffraction condition, and its aperture radius ρ and propagation distance R satisfy L c The coherence length modulation relationship is given by =Rλ / ρ, where L... c λ is the transverse coherence length, and λ is the average wavelength of the atomic beam.

5. The holographic lithography apparatus according to claim 1 or 4, wherein, The collimation stop is a circular stop. With an aperture ρ = 100-300 μm and a propagation distance R = 0.3-0.5 m, it outputs a collimated atomic beam with a transverse coherence ≥ 1 μm and a divergence angle ≤ 0.3 mrad.

6. The holographic lithography apparatus according to claim 1, wherein, The support layer of the holographic mask is made of a material with a low coefficient of thermal expansion and inertness to metastable helium atoms, such as one or more of silicon, borosilicate glass, AlN ceramic, and nickel-based alloys. Preferably, the holographic mask layer is made of a silicon nitride thin film, on which a nanoscale array of pores is formed for modulating the amplitude and phase of metastable helium atoms.

7. The holographic lithography apparatus according to claim 1, wherein, The metastable helium atom holographic lithography apparatus further includes a conical aperture disposed between the ground-state helium beam generating component and the electron excitation gun along the transmission path of the helium beam.

8. An atomic near-field holographic imaging method, comprising the following steps using the metastable helium atom holographic lithography apparatus according to any one of claims 1 to 7: (1) Provide photolithography sample: Coat the substrate surface with a self-assembled monolayer photoresist that is sensitive to metastable helium atoms to form a photolithography sample; (2) The helium gas in the helium source supply container is injected to generate a directional helium beam. The temperature adjustment module is used to adjust the wavelength of the helium beam to 0.05-0.22 nm by adjusting the temperature of the helium beam to provide a quasi-monochromatic ground state helium atom beam. (3) The ground-state helium atom is excited into a metastable helium atom using the electron excitation gun described above; (4) The collimating aperture is used to collimate the metastable helium atom beam to improve the transverse coherence of the metastable helium atom beam; (5) The collimated metastable helium atom beam is coherently irradiated on the holographic mask and holographically imaged on the self-assembled monolayer photoresist after passing through the nanopore array of the holographic mask layer, forming an exposure area with nanoscale resolution. (6) The exposed pattern is transferred to the substrate by wet etching to generate the target nanopattern.

9. The holographic imaging method according to claim 8, wherein, The functional molecules of the self-assembled monolayer photoresist are selected from organic molecules containing thiols and / or silane groups, preferably alkathiols or alkathiols modified with functional groups, such as one or more of dodecanethiol, octadecyltrichlorosilane, butanethiol, octylthiol, and heptanethiol.

10. The application of the metastable helium atom holographic lithography apparatus according to any one of claims 1 to 7 or the atomic near-field holographic imaging method according to claim 8 or 9 in semiconductor chip manufacturing.

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