A preparation system and a preparation method of a large-area phase type calculation hologram

Abstract

This invention discloses a fabrication system and method for large-area phase-type computational holograms. The method involves designing and constructing a fabrication system for large-area phase-type computational holograms. By utilizing a micromirror array and microlens array in the photoresist excitation optical path, tens of thousands of laser beams are generated for parallel writing, achieving an equivalent writing speed of 100 mm / s. The minimum lateral feature size of each beam reaches 50 nm, enabling the fabrication of large-area phase-type computational holograms. The designed large-area phase-type computational hologram employs a photonic sieve-like structure, which significantly improves the accuracy of surface shape detection compared to traditional zone plate-type computational holograms, enabling high-precision aspherical surface shape detection for extreme ultraviolet lithography objectives.

Description

Technical Field

[0001] This invention belongs to the field of optical precision manufacturing technology, specifically relating to a preparation system and method for large-area phase-type computational holograms. Background Technology

[0002] The lithography objective system is the most precise and complex subsystem in an extreme ultraviolet (EUV) lithography machine. With the increase in numerical aperture (NA), the precision requirements for high-steepness, large-deviation aspherical surfaces are also gradually increasing. For complex curved surfaces with surface shape errors across the entire aperture, sub-nanometer precision requirements have been proposed. Therefore, high-precision detection of the surface shape of optical components in EUV lithography objectives is a key issue.

[0003] Computational holograms (CGHs), based on optical diffraction theory, can generate reference wavefronts of arbitrary shapes and compensate for various types of aberrations, making them a core device for solving the problem of high-precision aspherical surface shape detection. Computational holograms can be divided into amplitude-type CGHs and phase-type CGHs. Compared to amplitude-type CGHs, phase-type CGHs modulate the phase of light, fully utilizing the energy of light at various points, resulting in higher diffraction efficiency and better meeting the requirements of ultra-high-precision aspherical objective lens surface shape detection.

[0004] Traditional phase-type CGH fabrication processes primarily employ electron beam writing or laser writing techniques. Electron beam writing offers high precision and is suitable for fabricating devices with minimum linewidths less than 0.5 μm, but its slow writing speed poses a significant challenge for large-area CGH manufacturing. Compared to electron beam writing, laser writing offers advantages such as lower cost, faster writing speed, simpler operation, and lower environmental requirements, making it a promising technology. However, it is limited by the optical diffraction limit, primarily used for devices with micron-level feature sizes. This significantly restricts further improvements in computational hologram accuracy, thus impacting the detection of higher-precision aspherical surfaces. Furthermore, laser writing has a slow single-point writing speed, while CGH sizes for extreme ultraviolet lithography objective surface detection are larger than 6 inches, resulting in fabrication times of several days and hindering large-scale application.

[0005] A Digital Micromirror Device (DMD) is an optical micro-electrical-mechanical system (MEMS) with electronic input and optical output. It consists of many small aluminum mirrors, each of which is called a pixel. Each mirror can deflect ±12° around the diagonal of each positively oriented micromirror (or pixel), meaning that the micromirrors of a DMD have three states: +12°, 0°, and -12°.

[0006] Based on semiconductor manufacturing technology, a digital mirror display (DMD) consists of a high-speed digital light reflection switch array. It determines the image pattern and its characteristics by controlling the rotation of micromirrors around a fixed (yoke) axis and their temporal response (which determines the reflection angle and dwell time of light). It is a novel, fully digital flat-panel display device that integrates a reflective micromirror array and CMOS SRAM onto a single chip using MEMS technology.

[0007] A microlens array is an array of lenses with apertures and relief depths on the order of micrometers. Like traditional lenses, its smallest functional unit can be a spherical mirror, aspherical mirror, cylindrical mirror, prism, etc., and it can also achieve focusing, imaging, and beam transformation functions at micro-optical angles. Because of its small unit size and high integration, it can form many novel optical systems, accomplishing functions that traditional optical elements cannot.

[0008] A single pixel in a DMD is 10.8 μm in size. In conventional laser direct writing schemes using DMDs, the DMD and the writing plane are usually conjugate, resulting in a minimum linewidth on the order of micrometers, which cannot break the diffraction limit. For example, the literature (Chan KF, Feng Z, Yang R, et al. High-resolution maskless lithography[J]. Journal of Micro / Nanolithography, MEMS, and MOEMS, Vol.2, Issue 4, October 2003) uses DMD laser direct writing to create a minimum linewidth of 1.5 μm. Summary of the Invention

[0009] This invention addresses the aforementioned shortcomings of existing technologies by providing a fabrication system and method for large-area phase-type computational holograms. Based on a highly uniform parallel two-photon lithography method using digital micromirror devices (DMDs) and microlens arrays (MLAs), this method can generate 10,000 femtosecond laser focal points with individual switching and intensity tuning capabilities, enabling simultaneous lithography with tens of thousands of beams in parallel, significantly improving the writing speed of direct-write lithography. Employing edge light suppression technology, it breaks through the writing resolution limitations of laser direct-write lithography systems, achieving a minimum lateral feature size of 50nm. Combined with a 12-inch 5-DOF mobile processing platform, it solves the manufacturing and processing requirements of existing large-area phase-type computational holograms.

[0010] This invention first provides a system for fabricating large-area phase-type computational holograms, including a photoresist excitation optical path for initiating photopolymerization of photoresist; a photoresist suppression optical path for inhibiting photopolymerization of photoresist; and a beam combining optical path for the photoresist excitation optical path and the photoresist suppression optical path.

[0011] The photoresist excitation optical path includes an excitation laser, a half-wave plate, a first polarizing beam splitter, a micromirror array, a first lens, a second lens, and a microlens array arranged sequentially along the optical path.

[0012] The excitation laser is used to emit excitation light. The excitation light is polarized by a half-wave plate, and the power of the excitation light entering the micromirror array is controlled by a first polarizing beam splitter. The first lens and the second lens form an optical 4f system, such that the surfaces of the micromirror array and the microlens array are conjugate.

[0013] The micromirror array includes multiple planar mirrors with controllable angles arranged in an array, and the microlens array includes multiple microlenses arranged in an array. By controlling each microlens in the microlens array, the corresponding planar mirror in the micromirror array can be controlled, so as to achieve independent power control of each parallel laser beam in the excitation light.

[0014] Preferably, the photoresist excitation optical path further includes a grating disposed between the first polarizing beam splitter and the micromirror array to compensate for the angular dispersion generated by the optical path; a first beam expander is disposed between the grating and the micromirror array to expand the beam of the excitation light.

[0015] Preferably, the micromirror array consists of 800,000 to 4,000,000 planar mirrors with controllable angles.

[0016] Each microlens in the microlens array corresponds to 100 to 200 planar mirrors in the microlens array.

[0017] In this invention, the DMD controls the light field in the frequency domain, and more than a hundred DMD pixels control the light intensity of a microlens beam. The focal plane of the microlens is conjugate with the writing plane, and a suppression light array is used to suppress two-photon excitation. This significantly increases the size of the writing feature while ensuring independent control of the light intensity of each beam.

[0018] Preferably, the photoresist suppression optical path includes a suppression laser, an acousto-optic modulator, a second beam expander, and a spatial light modulator arranged sequentially along the optical path.

[0019] The suppression laser is used to emit suppression light, the acousto-optic modulator is used to control the power of the suppression light, the second beam expander is used to expand the beam of the suppression light, and the spatial light modulator is used to modulate the phase of the suppression light.

[0020] More preferably, the photoresist-suppressed optical path further includes a reflector disposed between the second beam expander and the spatial light modulator.

[0021] Preferably, the photoresist excitation optical path further includes a third lens disposed downstream of the microlens array;

[0022] The beam combining optical path includes a second polarizing beam splitter, a fourth lens, a fifth lens, a first beam splitter, a dichroic beam splitter, a microscope objective, and a writing platform arranged sequentially along the optical path.

[0023] The third and fourth lenses form a 4f system, which conjugates the excitation light focused by the microlens array to the suppression light, and combines the suppression light and the excitation light to form a combined beam. The combined beam passes through the fifth lens, the first beam splitter, and the dichroic beam splitter in sequence before entering the microscope objective, and is finally focused onto the writing platform for photolithography.

[0024] The writing platform adopts a 12-inch air-bearing platform with five degrees of freedom: x-axis, y-axis, z-axis, x-direction rotation, and y-direction rotation. The x-axis and y-axis enable the moving scanning and writing of the writing plane, the z-axis enables real-time focusing and locking, and the x-direction rotation and y-direction rotation together ensure the perpendicularity of the writing plane to the z-axis direction of the objective lens, thereby enabling the writing and production of large-area computational holograms.

[0025] More preferably, the system for preparing the large-area phase-type computational hologram further includes a beam-combining imaging optical path for imaging the beam-combining light. The beam-combining imaging optical path includes a sixth lens and a first camera. The beam-combining light passes through a fifth lens, a first beam splitter, and a sixth lens in sequence before being imaged onto the first camera.

[0026] More preferably, the system for fabricating the large-area phase-type computational hologram further includes an illumination imaging optical path, which comprises an illumination source, a second beam splitter, a seventh lens, and a second camera.

[0027] The illumination light emitted by the illumination source is reflected by the second beam splitter and transmitted through the dichroic beam splitter into the microscope objective and illuminates the writing platform. Then the illumination light is back-reflected back into the microscope objective and sequentially passes through the dichroic beam splitter, the second beam splitter, and the seventh lens before being imaged onto the second camera.

[0028] This invention provides a method for preparing a large-area phase-type computational hologram, comprising the following steps:

[0029] (1) Deposit a Cr or CrO2 film on the substrate surface, and then coat the Cr or CrO2 film with photoresist.

[0030] (2) The pattern of the computational hologram is fabricated onto photoresist using the fabrication system for the large-area phase-type computational hologram;

[0031] (3) After the photoresist is exposed according to the pattern designed by the computational hologram, the soluble part is removed by solvent treatment, and the pattern is formed on the photoresist layer;

[0032] (4) Etch away the Cr or CrO2 film not covered by photoresist to expose the substrate surface; remove the remaining photoresist, clean and dry to obtain an amplitude-type computational hologram.

[0033] The photoresist used is capable of satisfying both two-photon excitation and single-photon suppression.

[0034] The excitation light uses a femtosecond pulsed laser with a wavelength of 515nm, and the suppression light uses a picosecond pulsed laser with a wavelength of 532nm. The 515nm femtosecond pulsed laser achieves two-photon absorption, while the 532nm picosecond pulsed laser achieves single-photon absorption suppression. Using a 12-inch 5-DOF air-bearing platform, an equivalent writing speed of 100mm / s can be achieved, and the minimum lateral feature size can reach 50nm.

[0035] Preferably, the large-area phase-type computational hologram design of the present invention adopts a photonic sieve form. Structurally, it uses a large number of micropores to replace the ring structure of the Fresnel zone plate. Compared with the traditional zone plate, it obtains a light spot with a smaller diameter than the outermost ring aperture, breaking through the limitation of processing level on resolution. It can also reduce the secondary size and decrease the side lobes of the focused light spot, resulting in higher detection accuracy and meeting the high-precision surface detection requirements of extreme ultraviolet lithography objectives.

[0036] More preferably, the computational hologram design pattern of the present invention is composed of an array of computational holographic units arranged like photon sieve micropores. The units at different positions have different sizes and are cylindrical in shape, with a minimum diameter of 50 nm. The laser direct writing scheme of the preparation method of the present invention changes the size of the effective writing beam by changing the power of the excitation light and the suppression light together, thereby completing the writing size control of the excitation light and realizing the precise writing of the phase-type CGH pattern.

[0037] This invention discloses a method for fabricating large-area phase-type computational holograms. By designing and constructing a fabrication system for large-area phase-type computational holograms, and utilizing a micromirror array and microlens array in the photoresist excitation optical path, tens of thousands of laser beams are generated for parallel writing, achieving an equivalent writing speed of 100 mm / s. The minimum lateral feature size of each beam reaches 50 nm, enabling the fabrication of large-area phase-type computational holograms. The designed large-area phase-type computational hologram employs a photonic sieve-like structure, which, compared to traditional zone plate-type computational holograms, significantly improves the accuracy of surface shape detection, enabling high-precision aspherical surface shape detection for extreme ultraviolet lithography objectives. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the optical path structure of the fabrication system for the large-area phase-type computational hologram of the present invention.

[0039] Figure 2 This is a schematic diagram of the photon-like sieve CGH of the present invention. Detailed Implementation

[0040] like Figure 1 As shown, a large-area phase-type computational hologram fabrication system is used for fabricating phase-type computational holograms for detecting the surface shape of extreme ultraviolet lithography objectives. The fabrication system of the present invention includes a photoresist excitation optical path for initiating a photopolymerization reaction of the photoresist; a photoresist suppression optical path for suppressing the photopolymerization reaction of the photoresist; and a beam combining optical path of the photoresist excitation optical path and the photoresist suppression optical path.

[0041] The photoresist excitation optical path includes an excitation laser 1, a half-wave plate 2, a first polarization beam splitter 3, a grating 4, a first beam expander 5, a micromirror array 6, a first lens 7, a second lens 8, a microlens array 9, and a third lens 10.

[0042] The excitation laser 1 uses a femtosecond laser, specifically a Ti:sapphire femtosecond laser, to provide the excitation light source. The wavelength is 515nm, the pulse width is 150fs, and the maximum output power is 20W.

[0043] The half-wave plate 2 is used to modulate the polarization direction of the femtosecond laser emitted from the femtosecond laser, and together with the subsequent first polarizing beam splitter 3, controls the excitation light power entering the optical system.

[0044] Grating 4 is used to compensate for the scattering caused by the optical path.

[0045] The first beam expander 5 is used to expand the light spot to match the effective aperture of the subsequent micromirror array 6.

[0046] The micromirror array 6, also known as a digital micromirror device (DMD), consists of 800,000 to 4 million planar mirrors with controllable angles, enabling pixel-by-pixel modulation of the beam illuminating it. For example, a DMD consisting of 1200×1980 planar mirrors with controllable angles can be used, totaling approximately 2.3 million planar mirrors. For higher precision and independent beam intensity control, a DMD with 2560×1600 pixels can be selected, totaling approximately 4 million planar mirrors. The first lens 7 and the second lens 8 form an optical 4f system, making the DMD surface conjugate to the surface of the microlens array 9. One microlens corresponds to 100–200 DMD pixels (one planar mirror is one pixel), for example, one microlens corresponds to 100, 150, or 200 DMD pixels. By controlling the on / off state of the DMD pixels corresponding to each lens, the power of the focused beam can be controlled, thereby achieving independent power modulation of all parallel laser beams.

[0047] The photoresist suppression optical path includes a suppression laser 12, an acousto-optic modulator 13, a second beam expander 14, a reflector 15, and a spatial light modulator 16.

[0048] The beam combining optical path includes a second polarizing beam splitter 11, a fourth lens 17, a fifth lens 18, a first beam splitter 19, a dichroic beam splitter 20, a microscope objective 21, and a writing platform 22.

[0049] The suppression laser 12 is a picosecond laser, which serves as the suppression light source, providing picosecond pulsed laser light with a wavelength of 532nm and a power of 5W. The acousto-optic modulator 13 controls the laser power, and then the laser beam is expanded by the second beam expander 14, and then enters the spatial light modulator 16 through the reflector 15 for phase modulation. The spatial light modulator 16 controls the wavefront of the suppression beam, so that the emitted suppression beam forms a suppression spot array after passing through the second polarization beam splitter 11 and the fourth lens 17.

[0050] The third lens 10 and the fourth lens 17 form a 4f system, which conjugates the laser array focused by the microlens array 9 to the suppression spot array, thus completing the beam focusing of the suppression light and the excitation light.

[0051] After being combined, the beam passes through the fifth lens 18, the first beam splitter 19, and the dichroic beam splitter 20 in sequence before entering the microscope objective 21, and is finally focused onto the writing platform 22 for photolithography.

[0052] The microscope objective 21 employs a 60x lens to focus the light beam onto the writing platform for laser writing. To match the objective's design, the system uses a photoresist with a refractive index of 1.52 to achieve dip-in writing. Compared to traditional oil-immersion objectives, this minimizes aberrations caused by refractive index inconsistencies and allows for writing on a variety of substrates.

[0053] The writing platform 22 adopts a 12-inch air-bearing platform with five degrees of freedom: x-axis, y-axis, z-axis, x-direction rotation, and y-direction rotation. The x-axis and y-axis enable the moving scanning and writing of the writing plane, the z-axis enables real-time focusing and locking, and the x-direction rotation and y-direction rotation together ensure the perpendicularity of the writing plane to the z-axis direction of the objective lens, thereby realizing the writing and fabrication of large-area computational holograms (CGH).

[0054] The large-area phase-type computational hologram fabrication system of the present invention also includes a beam-combining imaging optical path for imaging the combined beam. The beam-combining imaging optical path includes a sixth lens 23 and a first camera 24. The first camera 24 images the combined beam spot behind the fourth lens 17 through the fifth lens 18, the first beam splitter 19, and the sixth lens 23, realizing the monitoring of the quality and position of the combined beam spot, and providing a basis for conjugate surface assembly and spot alignment.

[0055] The large-area phase-type computational hologram fabrication system of the present invention further includes an illumination imaging optical path, which includes a second beam splitter 25, an illumination source 26, a seventh lens 27, and a second camera 28.

[0056] The illumination source 26 is a light-emitting diode (LED) with a wavelength of 589nm±10nm. The LED emits illumination light, which is reflected by the second beam splitter 25, transmitted through the dichroic beam splitter 20, and enters the microscope objective 21 to illuminate the writing platform 22. Subsequently, the illumination light is reflected back to the microscope objective 21 and sequentially passes through the dichroic beam splitter 20, the second beam splitter 25, and the seventh lens 27 to be imaged onto the camera 28, enabling real-time monitoring of the writing process.

[0057] The large-area phase-type computational hologram (CGH) fabrication system of this invention enables the writing of large-area phase-type CGHs. The main steps are as follows: A Cr or CrO2 film (80 nm thick) is deposited on the substrate surface, followed by a photoresist coating. A high-resolution direct-write lithography system using a 10,000-beam pulsed laser is used to fabricate the CGH pattern onto the photoresist. After exposure of the photoresist according to the CGH design pattern, the soluble portions are removed by solvent treatment, forming the pattern on the photoresist layer. An etching device is used to remove the Cr or CrO2 not covered by the photoresist, exposing the substrate surface. The remaining photoresist is removed, and the substrate is cleaned and dried to obtain an amplitude-type CGH, with some areas still containing the Cr or CrO2 film. The exposed substrate is etched again using an etching device to create steps of a certain depth, controlling the etching depth to the designed depth to achieve the required diffraction efficiency. The remaining residual Cr or CrO2 is cleaned to expose the entire substrate surface. The substrate is then dried to obtain the phase-type CGH.

[0058] The substrate is made of fused silica and is pretreated before applying the adhesive to ensure that the surface accuracy of the substrate meets the requirements.

[0059] The photoresist used is a specially formulated photoresist that can satisfy both two-photon excitation and single-photon suppression.

[0060] The large-area phase-type computational hologram design of this invention employs a photonic sieve, such as... Figure 2 In terms of structure, a large number of micro-holes are used to replace the ring structure of Fresnel zone plates. Compared with traditional zone plates, under the same minimum processing feature size, a spot with a smaller diameter than the outermost ring aperture can be obtained. This breaks through the limitation of processing level on resolution, and can reduce the secondary size and reduce the side lobes of the focused spot, resulting in higher detection accuracy and meeting the high-precision surface shape detection requirements of extreme ultraviolet lithography objectives.

[0061] The phase-type CGH design pattern consists of an array of computational holographic units arranged like micropores in a photon sieve. The units at different positions have different sizes and are cylindrical in shape, with a minimum diameter of 50 nm. The laser direct writing scheme of this method changes the size of the effective writing beam by changing the power of the excitation light and the suppression light together, thereby achieving the writing size control of the excitation light. Compared with the conventional scanning writing scheme, it avoids the polygonal cylinder caused by the scanning path and achieves precise writing of the phase-type CGH pattern.

Claims

1. A system for fabricating a large-area phase-type computational hologram, comprising a photoresist excitation optical path for initiating a photopolymerization reaction in photoresist; a photoresist suppression optical path for suppressing the photopolymerization reaction in photoresist; and a beam combining optical path for the photoresist excitation optical path and the photoresist suppression optical path, characterized in that, The photoresist excitation optical path includes an excitation laser, a half-wave plate, a first polarizing beam splitter, a micromirror array, a first lens, a second lens, and a microlens array arranged sequentially along the optical path. The excitation laser is used to emit excitation light. The excitation light is polarized by a half-wave plate, and the power of the excitation light entering the micromirror array is controlled by a first polarizing beam splitter. The first lens and the second lens form an optical 4f system, such that the surfaces of the micromirror array and the microlens array are conjugate. The micromirror array includes multiple planar mirrors with controllable angles arranged in an array, and the microlens array includes multiple microlenses arranged in an array. By controlling each microlens in the microlens array, the corresponding planar mirror in the micromirror array is controlled, thereby achieving independent power modulation of each parallel laser beam in the excitation light. The photoresist excitation optical path further includes a grating disposed between the first polarizing beam splitter and the micromirror array to compensate for the angular dispersion generated by the optical path; a first beam expander is disposed between the grating and the micromirror array to expand the beam of the excitation light. The photoresist excitation optical path also includes a third lens located downstream of the microlens array; The beam combining optical path includes a second polarizing beam splitter, a fourth lens, a fifth lens, a first beam splitter, a dichroic beam splitter, a microscope objective, and a writing platform arranged sequentially along the optical path. The third and fourth lenses form a 4f system, which conjugates the excitation light focused by the microlens array to the suppression light, thus combining the excitation and suppression light to form a combined beam. This combined beam then passes sequentially through the fifth lens, the first beam splitter, and the dichroic beam splitter before entering the microscope objective. Finally, it is focused onto the writing platform for photolithography. The photoresist suppression optical path includes a suppression laser, an acousto-optic modulator, a second beam expander, and a spatial light modulator arranged sequentially along the optical path. The suppression laser is used to emit suppression light, the acousto-optic modulator is used to control the power of the suppression light, the second beam expander is used to expand the beam of the suppression light, and the spatial light modulator is used to modulate the phase of the suppression light.

2. The system for preparing a large-area phase-type computational hologram according to claim 1, characterized in that, The micromirror array consists of 800,000 to 4,000,000 planar mirrors with controllable angles. Each microlens in the microlens array corresponds to 100 to 200 planar mirrors in the microlens array.

3. The system for preparing a large-area phase-type computational hologram according to claim 1, characterized in that, The photoresist-suppressed optical path also includes a reflector disposed between the second beam expander and the spatial light modulator.

4. The system for preparing a large-area phase-type computational hologram according to claim 1, characterized in that, It also includes a beam combining imaging optical path for imaging the beam combining light, the beam combining imaging optical path including a sixth lens and a first camera, the beam combining light passing through a fifth lens, a first beam splitter and a sixth lens in sequence before being imaged onto the first camera.

5. The system for preparing a large-area phase-type computational hologram according to claim 1, characterized in that, It also includes an illumination imaging optical path, which comprises an illumination source, a second beam splitter, a seventh lens, and a second camera. The illumination light emitted by the illumination source is reflected by the second beam splitter and transmitted through the dichroic beam splitter into the microscope objective and illuminates the writing platform. Then the illumination light is back-reflected back into the microscope objective and sequentially passes through the dichroic beam splitter, the second beam splitter, and the seventh lens before being imaged onto the second camera.

6. A method for preparing a large-area phase-type computational hologram, characterized in that, Includes the following steps: (1) Deposit a Cr or CrO2 film on the substrate surface, and then coat the Cr or CrO2 film with photoresist; (2) Using the fabrication system of any one of claims 1 to 5, the pattern of the computational hologram is fabricated onto the photoresist; (3) After the photoresist is exposed according to the pattern designed by the computational hologram, the soluble part is removed by solvent treatment, and the pattern is formed on the photoresist layer; (4) Etching removes the Cr or CrO2 film not covered by photoresist, exposing the substrate surface; Remove the remaining photoresist, clean and dry to obtain an amplitude-type computational hologram.

7. The method for preparing a large-area phase-type computational hologram according to claim 6, characterized in that, The photoresist used is capable of satisfying both two-photon excitation and single-photon suppression.

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