Talbot Lithography Research Articles

Large-scale fabrication of highly ordered sub-20\u2009nm noble metal nanoparticles on silica substrates without metallic adhesion layers

Periodic noble metal nanoparticles offer a wide spectrum of applications including chemical and biological sensors, optical devices, and model catalysts due to their extraordinary properties. For sensing purposes and catalytic studies, substrates made of glass or fused-silica are normally required as supports, without the use of metallic adhesion layers. However, precise patterning of such uniform arrays of silica-supported noble metal nanoparticles, especially at sub-100 nm in diameter, is challenging without adhesion layers. In this paper, we report a robust method to large-scale fabricate highly ordered sub-20 nm noble metal nanoparticles, i.e., gold and platinum, supported on silica substrates without adhesion layers, combining displacement Talbot lithography (DTL) with dry-etching techniques. Periodic photoresist nanocolumns at diameters of ~110 nm are patterned on metal-coated oxidized silicon wafers using DTL, and subsequently transferred at a 1:1 ratio into anti-reflection layer coating (BARC) nanocolumns with the formation of nano-sharp tips, using nitrogen plasma etching. These BARC nanocolumns are then used as a mask for etching the deposited metal layer using inclined argon ion-beam etching. We find that increasing the etching time results in cone-shaped silica features with metal nanoparticles on the tips at diameters ranging from 100 nm to sub-30 nm, over large areas of 3×3 cm2. Moreover, subsequent annealing these sub-30 nm metal nanoparticle arrays at high-temperature results in sub-20 nm metal nanoparticle arrays with ~1010 uniform particles.

3D-fabrication of tunable and high-density arrays of crystalline silicon nanostructures

In this report, a procedure for the 3D-nanofabrication of ordered, high-density arrays of crystalline silicon nanostructures is described. Two nanolithography methods were utilized for the fabrication of the nanostructure array, viz. displacement Talbot lithography (DTL) and edge lithography (EL). DTL is employed to perform two (orthogonal) resist-patterning steps to pattern a thin Si3N4 layer. The resulting patterned double layer serves as an etch mask for all further etching steps for the fabrication of ordered arrays of silicon nanostructures. The arrays are made by means of anisotropic wet etching of silicon in combination with an isotropic retraction etch step of the etch mask, i.e. EL. The procedure enables fabrication of nanostructures with dimensions below 15 nm and a potential density of 1010 crystals cm−2.

Refined grating fabrication using Displacement Talbot Lithography

High-resolution grating areas with none stitching error are in demanding needs but usually expensive and hard to prepare. In this paper, we present a method of making refined grating areas from coarse photolithography mask using Displacement Talbot Lithography (DTL). DTL is relatively simple and low-cost system based on mask photolithography for high-resolution periodic structures over large areas. The grating periods on the ordinary coarse photolithography mask was designed as 3.552μm. By patterning gratings on Si3N4 film deposited on fused silica as intervening phase masks, the final prepared grating periods shrinks 8 times, down to 444nm. This technology is suitable for producing large area high resolution gratings to reduce the research cost, and can be applied to applications such as DFB laser production, LED substrates preparation and other relative fields.

Hybrid Top‐Down/Bottom‐Up Fabrication of Regular Arrays of AlN Nanorods for Deep‐UV Core–Shell LEDs

Core–shell nanostructures are predicted to highly improve the efficiency of deep‐UV light emitting diodes (LEDs), owing to their low defect density, reduced quantum‐confined Stark effect, high‐quality non‐polar growth and improved extraction efficiency. In this paper, we report on the nanofabrication of high‐quality AlN nanorod arrays using a hybrid top‐down/bottom‐up approach for use as a scaffold for UV LED structures. We describe the use of Displacement Talbot Lithography to fabricate a metallic hard etch mask to allow AlN nanorod arrays to be dry etched from a planar AlN template. In particular, we investigate the impact of etching parameters on the nanorod etch rate, tapering profile and mask selectivity in order to achieve vertical‐sided nanorod arrays with high aspect ratios. AlN facet recovery is subsequently explored by means of regrowth using Metal Organic Vapor Phase Epitaxy. Low pressure and high V/III ratio promote straight and smooth sidewall faceting, which results in an improvement of the optical quality compared to the initial AlN template. The promising results open new perspectives for the fabrication of high‐efficiency deep‐UV‐emitting core–shell LEDs.

Optical properties and resonant cavity modes in axial InGaN/GaN nanotube microcavities

Microcavities based on group-III nitride material offer a notable platform for the investigation of light-matter interactions as well as the development of devices such as high efficiency light emitting diodes (LEDs) and low-threshold nanolasers. Disk or tube geometries in particular are attractive for low-threshold lasing applications due to their ability to support high finesse whispering gallery modes (WGMs) and small modal volumes. In this article we present the fabrication of homogenous and dense arrays of axial InGaN/GaN nanotubes via a combination of displacement Talbot lithography (DTL) for patterning and inductively coupled plasma top-down dry-etching. Optical characterization highlights the homogeneous emission from nanotube structures. Power-dependent continuous excitation reveals a non-uniform light distribution within a single nanotube, with vertical confinement between the bottom and top facets, and radial confinement within the active region. Finite-difference time-domain simulations, taking into account the particular shape of the outer diameter, indicate that the cavity mode of a single nanotube has a mixed WGM-vertical Fabry-Perot mode (FPM) nature. Additional simulations demonstrate that the improvement of the shape symmetry and dimensions primarily influence the Q-factor of the WGMs whereas the position of the active region impacts the coupling efficiency with one or a family of vertical FPMs. These results show that regular arrays of axial InGaN/GaN nanotubes can be achieved via a low-cost, fast and large-scale process based on DTL and top-down etching. These techniques open a new perspective for cost effective fabrication of nano-LED and nano-laser structures along with bio-chemical sensing applications.

State-of-the-art Nanofabrication in Catalysis.

We present recent developments in top-down nanofabrication that have found application in catalysis research. To unravel the complexity of catalytic systems, the design and use of models with control of size, morphology, shape and inter-particle distances is a necessity. The study of well-defined and ordered nanoparticles on a support contributes to the understanding of complex phenomena that govern reactions in heterogeneous and electro-catalysis. We review the strengths and limitations of different nanolithography methods such as electron beam lithography (EBL), photolithography, extreme ultraviolet (EUV) lithography and colloidal lithography for the creation of such highly tunable catalytic model systems and their applications in catalysis. Innovative strategies have enabled particle sizes reaching dimensions below 10 nm. It is now possible to create pairs of particles with distance controlled with an extremely high precision in the order of one nanometer. We discuss our approach to study these model systems at the single-particle level using X-ray absorption spectroscopy and show new ways to fabricate arrays of single nanoparticles or nanoparticles in pairs over a large area using EBL and EUV-achromatic Talbot lithography. These advancements have provided new insights into the active sites in metal catalysts and enhanced the understanding of the role of inter-particle interactions and catalyst supports, such as in the phenomenon of hydrogen spillover. We present a perspective on future directions for employing top-down nanofabrication in heterogeneous and electrocatalysis. The rapid development in nanofabrication and characterization methods will continue to have an impact on understanding of complex catalytic processes.

Shrinkage Control of Photoresist for Large‐Area Fabrication of Sub‐30 nm Periodic Nanocolumns

A method to fabricate large-area arrays of nanocolumns without a deep-UV laser source is reported. This method allows high-yield fabrication of 3 x 3 cm(2) arrays of sub-30 nm nanocolumns made of bottom antireflection layer coating (BARC) by combining displacement Talbot lithography (DTL) using a monochromatic UV beam (365 nm wavelength) with plasma etching techniques. DTL is used to manufacture an initial pattern of periodic photo-resist nanocolumns with a diameter of similar or equal to 110 nm. N-2 plasma can transfer this pattern at a 1: 1 ratio to BARC nanocolumns. It is found that reactive O-2/N-2 plasma etching on the other hand can shrink the BARC nanocolumns to sub-30 nm dimensions. The shrink-etching process can be reproducibly controlled by tuning the gas flow ratio and the etching time. It is highly remarkable that the verticality of these BARC nanocolumns remains during O-2/N-2 plasma shrink etching. Combining the etching of O-2/N-2 plasma with N-2 plasma allows to produce BARC nanocolumns over the entire diameter range from 110 to sub-30 nm. The fabrication approach enables large-footprint fabrication of size-tunable periodic nanostructures that have many potential applications in photonics, electronics, biosensors, smart surfaces, catalysis, and biomedical analysis

Influence of symmetry and duty cycles on the pattern generation in achromatic Talbot lithography

Achromatic Talbot lithography has been proved as a robust and high throughput technique for large area nanopatterning with controllable feature sizes and duty cycles. In this work, the influence of symmetry and duty cycles on the pattern generation has been investigated in detail. Compared with square lattice case, no lattice rotation and spatial frequency multiplication can be observed in hexagonal nanopattern generation. Uniform pattern distribution with a 20 nm feature size has been obtained in square and hexagonal lattices by the masks with 144 nm period and ∼50% duty cycle. For the exposure of mask with a smaller duty cycle, nonuniform dot size distribution has been obtained in the square lattice. While, by using a smaller duty cycle hexagonal lattice mask, a highly uniform periodic hexagonal nanopattern with a 10% duty cycle has been obtained. All the experimental results were consistent with the simulation work.

High rotational symmetry photonic structures fabricated with multiple exposure Displacement Talbot Lithography

Quasi-periodic structures with a high degree of rotational symmetry are desired for photonic applications because of their nearly isotropic optical response, in contrast to the highly directional behavior of periodic lattices. Here we introduce a method based on the superposition of periodic structures obtained by multiple exposure of a photomask with Displacement Talbot Lithography in which the photomask is rotated by a certain angle between exposures. The resulting structure can be considered as a Moiré pattern. High-quality patterns with 10 and 12-fold rotation symmetries and resolutions in the sub-micron to micron range are uniformly and reproducibly printed. The technique is suitable for the mass fabrication of wafer-scale quasi-periodic photonic patterns.

Shrinkage Control of Photoresist for Large‐Area Fabrication of Sub‐30 nm Periodic Nanocolumns

A method to fabricate large‐area arrays of nanocolumns without a deep‐UV laser source is reported. This method allows high‐yield fabrication of 3 × 3 cm2 arrays of sub‐30 nm nanocolumns made of bottom antireflection layer coating (BARC) by combining displacement Talbot lithography (DTL) using a monochromatic UV beam (365 nm wavelength) with plasma etching techniques. DTL is used to manufacture an initial pattern of periodic photoresist nanocolumns with a diameter of ≈110 nm. N2 plasma can transfer this pattern at a 1:1 ratio to BARC nanocolumns. It is found that reactive O2/N2 plasma etching on the other hand can shrink the BARC nanocolumns to sub‐30 nm dimensions. The shrink‐etching process can be reproducibly controlled by tuning the gas flow ratio and the etching time. It is highly remarkable that the verticality of these BARC nanocolumns remains during O2/N2 plasma shrink etching. Combining the etching of O2/N2 plasma with N2 plasma allows to produce BARC nanocolumns over the entire diameter range from 110 to sub‐30 nm. The fabrication approach enables large‐footprint fabrication of size‐tunable periodic nanostructures that have many potential applications in photonics, electronics, biosensors, smart surfaces, catalysis, and biomedical analysis.

Depth-of-Focus Determination for Talbot Lithography of Large-Scale Free-Standing Periodic Features

The depth-of-focus (DOF) is an important factor to influence the pattern quality but seldom treated in conventional contact or proximity lithography. One explicit formula for DOF prediction is analytically derived in the context of photolithography of periodic features (i.e., the Talbot lithography), in which wavefront aberrations contributed by all diffraction orders are considered. Besides the numerical elucidations, a direct photolithographic process is also customized for experimental demonstration. With strict DOF estimation based on the governing equation for thickness control of the resist coating, large-scale freestanding features of micromeshes with well-controlled perforation and steepness are fabricated.

High-resolution, high-aspect-ratio iridium–nickel composite nanoimprint molds

Nanoimprint molds are traditionally made from silicon. Silicon molds suffer from distinct disadvantages as they are brittle, prone to damage, scratch easily, and can only be used in a planar format. This has limited their use in higher throughput systems where flexible molds are required such as in roll-to-roll and roll-to-plate systems. Nickel (Ni) molds, which are now de-rigueur in both batch and roller nanoimprint processes, can be used to address these problems, but fabrication and durability issues limit their availability and effectiveness in production. In this report, the authors introduce a fabrication route that has the potential to overcome the fabrication, quality, and wear problems of Ni molds. The new process relies on atomic layer deposition to form a smooth and high-aspect ratio patterned layer of iridium (Ir) on a Ni substrate. A large area nanohole array mold was fabricated using displacement Talbot lithography to demonstrate this process. The authors show the use of such composite molds via a batch thermal imprinting process to fabricate 70 nm hole arrays onto polycarbonate templates with a ±10% tolerance in diameter between the polycarbonate and the composite mold, and less than 1% of defects.

Achromatic Talbot lithography with partially coherent extreme ultraviolet radiation: process window analysis

The main purpose of this work is the experimental determination of the process window for achromatic Talbot lithography with partially coherent extreme ultraviolet (EUV) radiation. This work has been performed using the EUV laboratory exposure tool. It consists of a discharge produced plasma source with a direct beam path to a phase-shifting transmission mask, avoiding losses due to additional optical components, the photoresist-coated wafer, and a positioning system for each component. Both the source and the mask are optimized for 11-nm wavelength. The process window has been identified by a systematic analysis of several exposure series. The optimization of exposure parameters resulted in 50-nm half-pitch of the wafer features using a transmission mask with a rectangular dot array of 70-nm half-pitch. The depth of field is found to be 20 μm, and it can be extended by spatial filtering. The exposure dose and mask–wafer distance are varied around their optimal values to estimate the process window, using defectivity of the pattern as a control parameter.

Displacement Talbot lithography nanopatterned microsieve array for directional neuronal network formation in brain-on-chip

Commercial microelectrode arrays (MEAs) for in vitro neuroelectrophysiology studies rely on conventional two dimensional (2D) neuronal cultures that are seeded on the planar surface of such MEAs and thus form a random neuronal network. The cells attaching on these types of surfaces grow in 2D and lose their native morphology, which may also influence their neuroelectrical behavior. Besides, a random neuronal network formed on this planar surface in vitro also lacks comparison to the in vivo state of brain tissue. In order to improve the present MEA platform with the above mentioned concerns, in this paper, the authors introduce a three dimensional platform for neuronal cell culturing, where a linear nanoscaffold is patterned on a microsieve array by displacement Talbot lithography (DTL) and reactive ion etching. Good pattern uniformity is achieved by the DTL method on the topographically prepatterned nonflat surface of the microsieve array. Primary cortical cells cultured on the nanopatterned microsieve array show an organized network due to the contact guidance provided by the nanoscaffold, presenting 47% of the total outgrowths aligning with the nanogrooves in the observed view of field. Hence, the authors state that this nanopatterned microsieve array can be further integrated into microsieve-based microelectrode arrays to realize an advanced Brain-on-Chip model that allows us to investigate the neurophysiology of cultured neuronal networks with specifically organized architectures.

Restorative Self-Image of Rough-Line Grids: Application to Coherent EUV Talbot Lithography

Self-imaging is a well-known optical phenomenon produced by diffraction of a coherent beam in a periodic structure. The self-imaging effect (or Talbot effect) replicates the field intensity at a periodic mask in certain planes, effectively producing in those planes an image of the mask. However, the effect has not been analyzed for a rough-line grid from the point of view of the fidelity of the image. In this paper, we investigate the restorative effect of the self-image applied to the lithography of gratings with rough lines. This paper is applied to characterize a Talbot lithography experiment implemented in the extreme ultraviolet. With the self-imaging technique, a mask with grid patterns having bumps randomly placed along the line edges reproduces a grid pattern with smoothed line edges. Simulation explores the approach further for the cases of sub-100-nm pitch grids.

Sub-wavelength printing in the deep ultra-violet region using Displacement Talbot Lithography

Printing of sub-100nm half-pitch periodic structures is demonstrated using Displacement Talbot Lithography (DTL) and a deep ultra-violet light source. DTL is a recently developed mask-based photolithography for forming high-resolution periodic structures over large areas using a relatively simple and low-cost system. A phase shift mask consisting of a 40×40mm2 transmission grating with a half-pitch of 150nm is fabricated by electron-beam lithography followed by reactive ion etching. The geometry of the phase grating is optimized by numerical simulation. Using this mask, dense line/space patterns and two-dimensional arrays of pillars, both with a half-pitch of 75nm, are printed onto silicon wafers. This new technique is suitable for uniform and high-throughput patterning of large-areas for such applications as moths-eye anti-reflective nanostructures, distributed feedback lasers, zeroth-order gratings, wire-grid polarizers and engineered substrates for LEDs.

Patterning of nanodot-arrays using EUV achromatic Talbot lithography at the Swiss Light Source and Shanghai Synchrotron Radiation Facility

Achromatic Talbot lithography (ATL) at extreme ultraviolet (EUV) wavelengths has been used to produce one or two-dimensional periodic patterns over large areas. In this work, an ATL transmission mask was used to perform EUV exposures at 13.5nm and 8.8nm illumination wavelengths at two different synchrotron facilities, to study the broadband nature of the method and the used mask as well as to investigate the influence of illumination parameters and experimental arrangements. The experiments were performed at the Swiss Light Source (SLS), PSI, Switzerland, and at the Shanghai Synchrotron Radiation Facility (SSRF), P. R. China. Achromatic Talbot lithography was proven to be a simple and robust interference lithography scheme for producing large area and high resolution patterns suitable for different wavelengths and for a variety of EUV sources and setups.

扫描积分塔尔博特光刻条纹质量影响因素模拟分析

扫描积分塔尔博特光刻条纹质量影响因素模拟分析

Spectrum-Integral Talbot Effect for UV Photolithography With Extended DOF

A route of spectrum-integral Talbot lithography (SITL) with extended depth-of-focus (DOF) for microfabrication of periodic structures was explored under broadband incoherent illumination in this letter. The transmitted diffraction fields by different spectral components integrate together to generate the successive periodicity since certain distance along the direction of propagation. The mechanism of DOF extension was derived and numerically elucidated using the spectrum of a practical ultraviolet source. Experiments of proximity lithography in term of the numeric results were performed to record the intensity distributions within the DOF area. Finally, the results reveal the validity of SITL and its potentials in high-fidelity lithography of periodic micropatterns with almost unlimited DOF and thus enhanced resolution.

Submicro-pillars and holes from the depth-wise Talbot images of a conical phase mask.

We construct two-dimensional arrays of submicro-pillars and holes from the depth-wise Talbot images of a conical phase mask in a photoactive layer prepared on a quartz substrate. In contrast to the conventional Talbot lithography employing only one image in the photoactive layer, two images of the phase mask are produced in a depth-wise manner such that the pillar patterns are in the primary image plane while the hole patterns in the secondary image plane according to the penetration depth of the exposure energy. The conical symmetry plays a critical role in producing the covariant patterns of the phase mask in the photoactive layer through the suppression of higher orders of diffraction. Our two image-type approach is simple and versatile for producing different kinds of periodic structures for photonic applications and surface engineering on a micrometer-to-nanometer scale.