X-ray Interference Lithography Research Articles

Fabrication of large-area photonic crystal-modified X-ray scintillator imager for optical coding imaging.

The limited pattern area of periodic nanostructures limits the development of practical devices. This study introduces an X-ray interference lithography (XIL) stitching technique to fabricate a large-area (1.5 cm × 1.5 cm) two-dimensional photonic crystal (PhC) on the YAG: Ce scintillator, which functions as an encoder in a high numerical aperture optical encoding imaging system to effectively capture high-frequency information. An X-ray imaging experiment revealed a substantial 7.64 dB improvement in the signal-to-noise ratio (SNR) across a large field of view (2.6 mm × 2.6 mm) and achieved comparable or superior image quality with half the exposure dose. These findings have significant implications for advancing practical applications of X-ray imaging.

Molecular Glass Resists Based on Tetraphenylsilane Derivatives: Effect of Protecting Ratios on Advanced Lithography

A series of t-butyloxycarbonyl (t-Boc) protected tetraphenylsilane derivatives (TPSi-Bocx, x = 60, 70, 85, 100%) were synthesized and used as resist materials to investigate the effect of t-Boc protecting ratio on advanced lithography. The physical properties such as solubility, film-forming ability, and thermal stability of TPSi-Bocx were examined to assess the suitability for application as candidates for positive-tone molecular glass resist materials. The effects of t-Boc protecting ratio had been studied in detail by electron beam lithography. The results suggest that the TPSi-Bocx resist with different t-Boc protecting ratios exhibit a significant change in contrast, pattern blur, and the density of bridge defect. The TPSi-Boc70% resist achieves the most excellent patterning capability. The extreme ultraviolet (EUV) lithography performance on TPSi-Boc70% was evaluated by using the soft X-ray interference lithography. The results demonstrate that the TPSi-Boc70% resist can achieve excellent patterning capability down to 20 nm isolated lines at 8.7 mJ/cm2 and 25 nm dense lines at 14.5 mJ/cm2. This study will help us to understand the relationship between the t-Boc protecting ratio and the patterning ability and supply useful guidelines for designing molecular resists.

Fabrication of high aspect ratio and tilted nanostructures using extreme ultraviolet and soft x-ray interference lithography

We demonstrate the fabrication of metal and dielectric nanostructures using interference lithography with extreme ultraviolet (EUV) and soft x-ray synchrotron radiation down to a 2.5 nm wavelength. These specific wavelengths are chosen because of the industrial relevance for EUV lithography and because they are in the vicinity of the oxygen absorption edge of the high-resolution hydrogen silsesquioxane photoresist, allowing for the exposure of thick layers. We investigate the requirements to fabricate such structures and demonstrate that tall metal nanostructures with aspect ratios up to 7 could be achieved by EUV interference lithography and subsequent electroplating. We use the unique depth-of-focus-free property of interference and achromatic Talbot lithography to fabricate uniformly tilted dielectric nanostructures.

A new type of nanoscale reference grating manufactured by combined laser-focused atomic deposition and x-ray interference lithography and its use for calibrating a scanning electron microscope

Calibration of magnification and nonlinearity of scanning electron microscopy (SEM) is an essential task. In this paper, we proposed a new type of 1D grating sample fabricated by combining laser-focused atomic deposition and x-ray interference lithography as a lateral standard for calibrating SEMs. The calibrations of the grating pattern by a metrological large-range atomic force microscope indicate that the grating sample exhibits outstanding pattern uniformity that surpasses conventional samples fabricated by e-beam lithography: (1) the nonlinear deviation of the grating structures is below +/- 0.5 nm over a measurement range of 5 µm; (2) the maximal variation of the calibrated mean pitch values is lower than 0.01 nm at different locations randomly selected all over the pattern area. The proposed new sample is applied for accurately calibrating the magnification and nonlinearity of a commercial SEM, showing its advantages of easy-of-use and high accuracy. The influence of the defocus level of SEM on the calibration result is also demonstrated. This research offers a feasible solution for highly accurate SEM calibration needed for 3D nanometrology and hybrid metrology demanded in metrology of modern nanoelectronics devices and systems.

Analysis of partially coherent light propagation through the soft X-ray interference lithography beamline at SSRF.

The mutual optical intensity (MOI) model is extended to the simulation of the interference pattern produced by extreme ultraviolet lithography with partially coherent light. The partially coherent X-ray propagation through the BL08U1B beamline at Shanghai Synchrotron Radiation Facility is analysed using the MOI model and SRW (Synchrotron Radiation Workshop) method. The fringe intensity at the exposure area is not uniform but has similar envelope lines to Fresnel diffraction, which is explained by the diffraction from the finite grating modelled as a single aperture. By balancing the slit size and photon stop size, the fringe visibility, photon flux and intensity slope can be optimized. Further analysis shows that the effect of pink light on the aerial images is negligible, whereas the third-harmonic light should be considered to obtain a balance between high fringe visibility and high flux. Two grating interference exposure experiments were performed in the BL08U1B beamline. The aerial image depth showed that the polymethyl methacrylate photoresist depth was determined by the X-ray coherence properties.

Significant Enhancement in Light Output of Photonic-Crystal-Based YAG:Ce Scintillator for Soft X-Ray Detectors

Because of its high light output, Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S:Tb (P43) phosphor powder is widely used in scintillator detectors for scanning transmission soft X-ray microscopy. However, the long decay time (>1 ms) of P43 phosphor powder limits the image scanning speed. Inorganic scintillators such as YAG:Ce are very suitable for fast scanning imaging due to their short decay time (tens of nanoseconds). Nevertheless, its light output is lower than that of P43 phosphor powder. Patterning photonic crystals (PhCs) on the output surface of an inorganic scintillator is a simple and efficient method to enhance its light output. In this article, we use a soft X-ray interference lithography technique to produce a large-area pattern of nanoscale PhCs on a 200-μm -thickness and 1-in-diameter YAG:Ce scintillator. Measurement of the enhancement ratio was performed on the soft X-ray beamline (BL08U1A) at the Shanghai Synchrotron Radiation Facility. The results show that the light output of the PhC-patterned YAG:Ce scintillator with air coupling is approximately 2.8 times higher than that of the unpatterned YAG:Ce scintillator. Meanwhile, the time-resolved emission with optical excitation showed that the PhC structures did not affect the spontaneous emission rate in the internal of scintillator crystal. This enhancement of the light output indicates that the PhC-patterned YAG:Ce scintillator is a good candidate for soft X-ray detection.

The wave optical whole process design of the soft X-ray interference lithography beamline at SSRF.

A new spatially coherent beamline has been designed and constructed at the Shanghai Synchrotron Radiation Facility. Here, the design of the beamline is introduced and the spatial coherence is analyzed throughout the whole process by wave optics. The simulation results show good spatial coherence at the endstation and have been proven by experiment results.

Fabrication of large-area high-aspect-ratio periodic nanostructures on various substrates by soft X-ray interference lithography

Abstracts Periodic nanostructures have attracted considerable interest and been applied in many fields. However, nanostructures of sufficiently large areas and depths are necessary for the development of practical devices. In this study, large-area high-aspect-ratio periodic nanostructures were fabricated by using a hybrid technology based on X-ray interference lithography, and then the patterns were transferred onto various substrates successfully. The final periodic nanostructures on the substrate attained measurements up to square centimetres with depths greater than 200 nm.

Fabrication of high aspect ratio nanoscale periodic structures by the soft X-ray interference lithography

Nanoscale periodic structures have been utilized in the scintillator field to obtain enhanced light extraction efficiency. Sufficient structure depth is necessary to achieve better extraction efficiency. Recently, a soft X-ray interference lithography (SXIL) has been developed in the Shanghai Synchrotron Radiation Facility (SSRF). SXIL can be used to fabricate a high aspect ratio pattern due to the uniform distribution of the beam dose at the photoresist depth. A grating mask with a new photon stop layer was attempted, mainly consisting of Perm alloy, and it was optimized for the SXIL to increase the entire service life. Preliminary results suggest that PMMA structure with an aspect ratio of up to 3 has been successfully manufactured using SXIL techniques. Therefore, this technique has been studied to fabricate the artificial nanostructure on the scintillator in the high efficiency radiation detector area.

Dynamic absorption coefficients of chemically amplified resists and nonchemically amplified resists at extreme ultraviolet

The dynamic absorption coefficients of several chemically amplified resists (CAR) and non-CAR extreme ultraviolet (EUV) photoresists are measured experimentally using a specifically developed setup in transmission mode at the x-ray interference lithography beamline of the Swiss Light Source. The absorption coefficient α and the Dill parameters ABC were measured with unprecedented accuracy. In general, the α of resists match very closely with the theoretical value calculated from elemental densities and absorption coefficients, whereas exceptions are observed. In addition, through the direct measurements of the absorption coefficients and dose-to-clear values, we introduce a new figure of merit called chemical sensitivity to account for all the postabsorption chemical reaction ongoing in the resist, which also predicts a quantitative clearing volume and clearing radius, due to the photon absorption in the resist. These parameters may help provide deeper insight into the underlying mechanisms of the EUV concepts of clearing volume and clearing radius, which are then defined and quantitatively calculated.

Development of broadband X-ray interference lithography large area exposure system.

The single-exposure patterned area is about several 10(2) × 10(2) μm(2) which is mainly decided by the mask area in multi-beam X-ray interference lithography (XIL). The exposure area is difficult to stitch to a larger one because the patterned area is surrounded by 0th diffraction exposure areas. To block the 0th diffraction beams precisely and effectively, a new large area exposure technology is developed in the Shanghai Synchrotron Radiation Facility by applying an order-sorting aperture with a new in situ monitoring scheme in the XIL system. The patterned area could be stitched readily up to several square centimeters and even bigger by this technology.

Fabrication of Thiol-Ene "Clickable" Copolymer-Brush Nanostructures on Polymeric Substrates via Extreme Ultraviolet Interference Lithography.

We demonstrate a new approach to grafting thiol-reactive nanopatterned copolymer-brush structures on polymeric substrates by means of extreme ultraviolet (EUV) interference lithography. The copolymer brushes were designed to contain maleimide functional groups as thiol-reactive centers. Fluoropolymer films were exposed to EUV radiation at the X-ray interference lithography beamline (XIL-II) at the Swiss Light Source, in order to create radical patterns on their surfaces. The radicals served as initiators for the copolymerization of thiol-ene "clickable" brushes, composed of a furan-protected maleimide monomer (FuMaMA) and different methacrylates, namely, methyl methacrylate (MMA), ethylene glycol methyl ether methacrylate (EGMA), or poly(ethylene glycol) methyl ether methacrylate (PEGMA). Copolymerization with ethylene-glycol-containing monomers provides antibiofouling properties to these surfaces. The number of reactive centers on the grafted brush structures can be tailored by varying the monomer ratios in the feed. Grafted copolymers were characterized by using attenuated total reflection infrared (ATR-IR) spectroscopy. The reactive maleimide methacrylate (MaMA) units were utilized to conjugate thiol-containing moieties using the nucleophilic Michael-addition reaction, which proceeds at room temperature without the need for any metal-based catalyst. Using this approach, a variety of functionalities was introduced to yield polyelectrolytes, as well as fluorescent and light-responsive polymer-brush structures. Functionalization of the brush structures was demonstrated via ATR-IR and UV-vis spectroscopy and fluorescence microscopy, and was also indicated by a color switch. Furthermore, grafted surfaces were generated via plasma activation, showing a strongly increased wettability for polyelectrolytes and a reversible switch in static water contact angle (CA) of up to 18° for P(EGMA-co-MaMA-SP) brushes, upon exposure to alternating visible and UV-light irradiation.

Large-scale uniform Au nanodisk arrays fabricated via x-ray interference lithography for reproducible and sensitive SERS substrate

Large-scale Au nanodisk arrays on Si substrate are successfully fabricated via x-ray interference lithography and followed by electron-beam vapor deposition. The Au nanodisk arrays exhibit a significant, uniform, and reproducible surface enhancement on Raman scattering signal, which enables the detection of R6G as low as 10−8 M with an enhancement factor of 106. Importantly, the Au nanodisk arrays SERS-active substrates with uniformly high sensitivity also have high reproducibility and stability. The diameters of the nanodisks and the inter-disk distance can be simply optimized to obtain high enhancement in Raman signal by varying exposure time and development time in XIL process. The electric fields of the Au nanodisks with various diameters and inter-disk distance simulated by the finite difference time domain (FDTD) techniques further confirm that the Raman signal enhancement of Au nanodisks is determined by the diameters of nanodisks and the inter-disk distance of nanodisks. The Au/Ag double-layer bimetal nanodisk arrays are also fabricated which show a significant increase in the Raman signal enhancement than that of the Au nanodisk arrays. XIL nanofabrication appears to be a feasible approach to prepare uniform and reproducible SERS-active substrates with high sensitivity for practical SERS applications.

X射线干涉光刻光束线偏转镜系统的设计与测试

The X-ray interference lithography(XIL)beamline at Shanghai Synchrotron Radiation Facility was introduced.To achieve the beam deflection and optical pathway switch of the beamline,a deflecting mirror system of XIL beamline was designed.The function of the deflecting mirror system was analyzed and its adjusting mechanism,switching mechanism and cooling structure were designed respectively.The key movement of adjusting mechanism was discussed,which is the translating process of a linear motion outside the mirror chamber into a rotary motion in ultra high vacuum.Then,the relationship between repeatability and carrying capacity of the switching mechanism was analyzed,and the strength of precision screw was checked.A cooling structure was designed by integrating a mirror support mode and a cooling mode,and the cooling effect was analyzed by numerical simulation method.The simulated results show that the meridian direction slope error and the sagittal direction slope error of the deflection mirror are about 6.5rad and 7rad respectively.The precisions of adjus-ting mechanism and switching mechanism were tested by a laser interferometer and a photoelectric autocollimator,and testing results show that linear resolution capability of adjusting mechanism is up to0.2μm,and the repeatability of switching mechanism satisfies the technical demands.

Structure Design and Numerical Simulation of a High Performance Slit in Soft X-Ray Interference Lithography Beamline at SSRF

A high precision slit in ultra-high vacuum is designed to develop a good performance soft X-ray interference lithography (XIL) beamline at Shanghai Synchrotron Radiation Facility (SSRF). In order to define the secondary source and enhance the performance of the beamline, many technical difficulties need resolving to design the precision slit. Therefore, to obtain reasonable design scheme, it is necessary to analyze the structural characteristics, the movement situation, the force state, the thermal load state, and the cooling state of the precision slit deeply by numerical simulation. The simulation results and the testing results demonstrate that the mechanical precision of the slit is at a high level and satisfies the requirements of the beamline.

Infrared photoluminescence of erbium-tris(8-hydroxyquinoline) in a distributed feedback cavity

A distributed feedback (DFB) waveguide cavity with erbium-tris(8-hydroxyquinoline) has been fabricated by X-ray interference lithography in a laboratory-scale apparatus. The DFB cavity consists of a large area (∼8mm2) one-dimensional grating of polymethylmethacrylate on Si (100). Structural, morphological and optical properties of the device have been studied. On-grating narrowing of the photoluminescence emission has been observed for the 492nm grating period in correspondence to the 4f–4f Er band peak (at 1530nm), indicating the possibility of optical gain for applications in the telecommunications.

Extreme Ultraviolet Interference Lithography for Generation of Platinum Nanoparticles on Glassy Carbon

In order to investigate corrosion processes of a catalyst and/or its support in polymer electrolyte fuel cells (PEFC), model electrodes consisting of platinum upon glassy carbon (GC) were produced via extreme ultraviolet interference lithography (EUV-IL) and subsequent platinum deposition. The exposure experiments were performed at the X-ray Interference Lithography (XIL) beamline of Swiss Light Source (SLS). The influence of exposure parameters (e.g. dose, thickness of the photoresist, amount of deposited platinum) and pre-treatment of the GC substrate upon the size of produced nanostructures and their adhesion to the surface was closely monitored using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The diameter of obtained Pt nanodots was 40-100 nm. It was found that the diameter of the obtained Pt nanodots was only dependent on the EUV dose. Thermal pre-treatment of GC had no obvious influence on the process steps.

13.4 nm软X射线干涉光刻透射光栅的优化设计

13.4 nm软X射线干涉光刻透射光栅的优化设计

The design, fabrication and performance of a large area 10000 line/mm metal transmission diffraction gratings for soft X-ray

Based on the rigorous coupled-wave analysis, the optimized design for a transmission two-gratings mask for 13.4nm soft X-ray interference lithography has been accomplished. Then a large area transmission gratings was successfully fabricated by electron beam lithography (EBL), which has an area of 1.5mm×1.5mm, ruling period of 100nm, Cr relief thickness of 50nm, gap/period of 0.6, and Si3N4 substrate thickness of 100nm. Based on the quantitative estimation of the measurement data, the first and second order diffraction efficiencies were determined as 4.41% and 0.49%, respectively， in good agreement with the numerical simulation results. Through comparison between the measurement and the numerical simulation results, it was shown that the relief is entirely vertical and the gap/period was well controlled. This two-grating mask will be used installed on the soft X-ray interference lithography endstation at Shanghai Synchrotron Radiation Facility (SSRF). With its 1st and 2nd order diffraction, 50nm period and 25nm period gratings can be cost-effectively fabricated, respectively.

Arrays of nanoscale magnetic dots: Fabrication by x-ray interference lithography and characterization

X-ray interference lithography (XIL) was employed in combination with electrodeposition to fabricate arrays of nanoscale nickel dots which are uniform over 40μm and have periods down to 71nm. Using extreme-ultraviolet light, XIL has the potential to produce magnetic dot arrays over large areas with periods well below 50nm, and down to a theoretical limit of 6.5nm for a 13nm x-ray wavelength. In the nickel dot arrays, we observed the effect of interdot magnetic stray field interactions. Measuring the hysteresis loops using the magneto-optical Kerr effect, a double switching via the vortex state was observed in the nickel dots with diameters down to 44nm and large dot separations. As the dot separations are reduced to below around 50nm a single switching, occurring by collective rotation of the magnetic spins, is favored due to interdot magnetic stray field interactions. This results in magnetic flux closure through several dots which could be visualized with micromagnetic simulations. Further evidence of the stray field interactions was seen in photoemission electron microscopy images, where bands of contrast corresponding to chains of coupled dots were observed.