High-efficiency binary phase-transmission-grating using e-beam lithography

Abstract

Rigorous coupled-wave analysis indicates that diffraction efficiencies greater than 99% are feasible for dielectric phase-gratings with a rectangular profile. The use of rectangular rather than blazed profiles implies simplified fabrication techniques, since deep-etch submicrometre structuring techniques can be utilized. We identify several parameter combinations with high diffraction efficiencies using rigorous coupled wave analysis, demonstrate experimentally diffraction efficiencies of 94% in a Bragg mount configuration at a wavelength of 543 nm and discuss the influence of substrate thickness on the transmitted light intensities. A direct writing electron-beam lithography fabrication process gives wide flexibility in design realization.     

Dip-pen lithography using pens of different thicknesses

A laboratory method to produce AFM tips of different sizes has been developed based on laser irradiation of the commercial silicon nitride tips. A few shots of 60 mJ at 355 nm were found adequate to induce the desired bluntness from 40 nm to 500 nm in a controlled way. Dip-pen nanolithography (DPN) has been performed with the blunt tips using a colloidal ink consisting of Pd nanocrystals coated with polyvinyl pyrrolidone. The line patterns drawn bear a direct relation with the tip morphology, wider the tip, broader are the patterns, in general. The rate of deposition also increases with the tip dimension, but is not as much proportional for larger tips. The study highlights the potential ability of DPN in integrating nano and microelectronics.     

Polymer pen lithography using dual-elastomer tip arrays

Dual-elastomer tip arrays are developed as a simple and cost-effective approach to significantly improve the uniformity and precision of polymer pen lithography (PPL). Both experiment and mechanical simulation demonstrate that the hard-apex, soft-base tip structure of the dual-elastomer tip array leads to precise control of feature size and reduced variation among different tips over large areas through fine control of the tip deformation. The dual-elastomer tip array is believed to be readily applied to fabricate nano- and microstructures for fundamental study and applications such as bioassays, sensors, optical and electronic devices.     

Nano-pillars using electron beam lithography and electroplating

##正##Mechanical testing of submicrometer-sized metal pillars has shown significant strengthening on decreasing the pillar dimensions. Analysis of such experiments is complicated, however, because the traditional focused ion beammethod for making the     

Formation of nanometer-scale structures using conventional optical lithography

We investigated a new method to form the line-and-space patterns with a nanometer-scale using the conventional optical lithography technique and the metal deposition/liftoff process. The ashing of the negative photo resist defined by the conventional optical lithography technique results in the proper profiles including a high aspect ratio (i.e., height/width value of the patterns) for the formation of nanometer-scale structures. We demonstrated that the metal electrodes with the nanometer-scale gap of 20 nm or less can be easily obtained by the newly proposed method without employing the highly sophisticated lithography tools including an electron beam lithography.     

Sub-10 nm patterning using EUV interference lithography

Extreme ultraviolet (EUV) lithography is currently considered as the leading technology for high-volume manufacturing below sub-20 nm feature sizes. In parallel, EUV interference lithography based on interference transmission gratings has emerged as a powerful tool for industrial and academic research. In this paper, we demonstrate nanopatterning with sub-10 nm resolution using this technique. Highly efficient and optimized molybdenum gratings result in resolved line/space patterns down to 8 nm half-pitch and show modulation down to 6 nm half-pitch. These results show the performance of optical nanopatterning in the sub-10 nm range and currently mark the record for photon-based lithography. Moreover, an efficient phase mask completely suppressing the zeroth-order diffraction and providing 50 nm line/space patterns over large areas is evaluated. Such efficient phase masks pave the way towards table-top EUV interference lithography systems.     

Writing an arbitrary non-periodic pattern using interference lithography

Abstract

We propose a technique to write non-periodic patterns using interference lithography. Arbitrary patterns in one and two dimension are constructed by continuous scanning of multiple coherent sources at various incident angles and intensities.     

Recent developments in nanofabrication using ion projection lithography

Ion projection lithography (IPL) is an emerging technology and a major candidate for the next-generation lithography (NGL) designed to complement and supplement current optical lithographic techniques for future chip manufacturing. In this Review, the recent developments of IPL technology are examined with an emphasis on its ability to fabricate a wide variety of nanostructures for the semiconductor industry. Following an introduction of the uniqueness and strength of the technology, the basics of ion-source development and ion-target interactions with and without chemical enhancement are presented. The developments in equipment systems, masks, and resists are subsequently studied. The resolution of printed nanostructures and the corresponding throughput of the current system are assessed for NGL. Finally, concluding remarks are presented to summarize the strengths and weaknesses of the current technology and to suggest the scope for future improvement.     

Vacuum lithography using plasma polymerization and plasma development

A completely dry lithography has been proposed which involves plasma polymerization of methyl methacrylate (MMA) and plasma development with CCl₄. It was called vacuum lithography because all processes were performed in a vacuum. However, the developed pattern had a lower resolution than patterns produced by conventional lithography with a wet process. After several technical refinements, the quality of the resist and the developed pattern was markedly improved. In this paper, recent results will be reported.A gas-flow-type reactor was used instead of a bell-jar-type reactor because the morphology of plasma-polymerized MMA (PPMMA) varied with each experimental run which was performed with the same gas and discharge parameters. The monomer vapour was introduced downstream of the argon discharge, and the polymerized film was formed on the substrate placed further downstream in the mixed gas.The development of pattern was performed by etching with an Ar-O₂ mixture and with hydrogen gas instead of CCl₄ gas, because the etching rate of the resist was too high in a CCl₄ plasma and a clear pattern was not obtained. The evaluated sensitivity and γ value of PPMMA were 1000 μC cm^?2 and 1 respectively. MMA containing 5% tetramethyltin was also used as a monomer gas for plasma polymerization downstream of the argon discharge. In this case the sensitivity and γ value were 10 μC cm^?2 and 2 respectively.     

High-fidelity replication of Dammann gratings using soft lithography

We report the experimental results of using the soft lithography method for replication of Dammann gratings. By using an elastomeric stamp, uniform grating structures were transferred to the UV-curable polymer. To evaluate the quality of the replication, diffraction images and light intensity were measured. Compared with the master devices, the replicas of Dammann gratings show a slight deviation in both surface relief profile and optical performance. Experimental results demonstrated that high-fidelity replication of Dammann gratings is realized by using soft lithography with low cost and high throughput.     

Security printing of covert quick response codes using upconverting nanoparticle inks

Counterfeiting costs governments and private industries billions of dollars annually due to loss of value in currency and other printed items. This research involves using lanthanide doped β-NaYF(4) nanoparticles for security printing applications. Inks comprised of Yb(3+)/Er(3+) and Yb(3+)/Tm(3+) doped β-NaYF(4) nanoparticles with oleic acid as the capping agent in toluene and methyl benzoate with poly(methyl methacrylate) (PMMA) as the binding agent were used to print quick response (QR) codes. The QR codes were made using an AutoCAD file and printed with Optomec direct-write aerosol jetting(?). The printed QR codes are invisible under ambient lighting conditions, but are readable using a near-IR laser, and were successfully scanned using a smart phone. This research demonstrates that QR codes, which have been used primarily for information sharing applications, can also be used for security purposes. Higher levels of security were achieved by printing both green and blue upconverting inks, based on combinations of Er(3+)/Yb(3+) and Tm(3+)/Yb(3+), respectively, in a single QR code. The near-infrared (NIR)-to-visible upconversion luminescence properties of the two-ink QR codes were analyzed, including the influence of NIR excitation power density on perceived color, in term of the CIE 1931 chromaticity index. It was also shown that this security ink can be optimized for line width, thickness and stability on different substrates.     

Large-area pattern transfer of metallic nanostructures on glass substrates via interference lithography

In this paper, we report a simple and effective nanofabrication method for the pattern transfer of metallic nanostructures over a large surface area on a glass substrate. Photoresist (PR) nano-patterns, defined by laser interference lithography, are used as template structures where a metal film of controlled thickness is directly deposited and then transferred onto a glass substrate by the sacrificial etching of the PR inter-layer. The laser interference lithography, capable of creating periodic nano-patterns with good control of their dimensions and shapes over a relatively large area, allows the wafer-scale pattern transfer of metallic nanostructures in a very convenient way. By using the approach, we have successfully fabricated on a glass substrate uniform arrays of hole, grating, and pillar patterns of Ti, Al, and Au in varying pattern periodicities (200 nm-1 μm) over a surface area of up to several cm(2) with little mechanical crack and delamination. Such robust metallic nanostructures defined well on a transparent glass substrate with large pattern coverage will lead to advanced scientific and engineering applications such as microfluidics and nanophotonics.     

Fabrication of zinc oxide nanostructures using solvent-assisted capillary lithography

We present a simple solvent-assisted capillary molding method to fabricate zinc oxide (ZnO) nanostructures using an ultraviolet (UV) curable polyurethane acrylate (PUA) mold. A thin film of the ZnO sol-gel precursor solution in methyl alcohol was prepared by spin coating on a solid substrate and subsequently a nanopatterned PUA mold was brought into conformal contact with the substrate under slight physical pressure (～3.5?bar). After annealing at 230?°C for 4?h, well-defined ZnO nanostructures formed with feature size down to ～50?nm, aided by capillary rise and solvent evaporation. It was found that the height of capillary rise depended highly on the applied pressure. A simple experimental setup was devised to examine the effects of pressure, revealing that the optimum pressure ranged from 3.5?bar to 5?bar. Also, ZnO nanorods could be selectively grown on patterned regions using the seed layer as a pseudocatalyst when the width of the seed layer was larger than ～200?nm.     

Towards creation of iron nanodots using metastable atom lithography

Iron structures with dimensions of the order of the minimum domain size (～50?nm at room temperature) may provide us with a new high-density data storage method. Limitations have been observed in existing depositional atom lithography schemes for producing these structures. We present a proof-in-principle experiment using an alternative scheme based upon direct exposure metastable neon-atom lithography. Iron structures with dimensions of the order of 7.5?μm are produced by this method. Extension of this work to the application of standing-wave atom lithography and laser cooling flux enhancement techniques is discussed as a method for reducing dimensions to a size equating to a dot array density of around 0.1?Gbit?mm(-2).     

Characterization of printed pigment-based inks on ink-jet media using cross-sectional electron microscopy

This paper reports on the microscopic assessment of representative specimen cross-sections prepared by microtomy and ultramicrotomy with emphasis in structure–property information using optical, scanning and transmission electron microscopy, namely, the absolute optical density δ, the measured effective printing coverage , the averaged pigment-based ink layer thickness , and the morphology at 100% nominal printing coverage. This work shows that for different test patches printed at the same nominal printing coverage a number of different printing schemes yield a pre-defined absolute optical density δ which basically depends on the measured effective printing coverage and the type of pigment-based inks used (spectral absorptivity m≠∞) and therefore on the averaged pigment-based ink layer thickness . A method for estimating the spectral absorptivity m is presented which combines the absolute optical density δ of the test patch and the averaged pigment-based ink layer thickness as measured from cross-sectional electron microscopy.     

Pollution-preventing anionic lithographic inks

Lithographic printing presses use aliphatic and aromatic solvents for cleaning various surfaces, which are coated with the ink. The conventional printing inks also contain volatile solvents. During printing and cleaning operations, volatile organic compounds (VOCs) present in the inks and cleaning solvents are lost to the atmosphere by evaporation and these losses are quantifiable and alarmingly high. A new type of ink based on castor oil, which completely eliminates emissions of VOCs, has been developed. Synthesis of resins and the kinetics of washing of the ink, similar to the recently announced pollution-preventing ink [development of a VOC-free lithographic printing system. TAGA Proc., 324], with water at a slightly elevated pH are studied. A correlation between the mass-transfer coefficient characterizing the washing of ink and the experimental process variables is confirmed. New data are also reported on flake-formation dynamics.     

Investigation on fabrication of nanoscale patterns using laser interference lithography

Nanoscale patterns are fabricated by laser interference lithography (LIL) using Lloyd's mirror interferometer. LIL provides a patterning technology with simple, quick process over a large area without the usage of a mask. Effects of various key parameters for LIL, with 257 nm wavelength laser, are investigated, such as the exposure dosage, the half angle of two incident beams at the intersection, and the power of the light source for generating one or two dimensional (line and dot) nanoscale structures. The uniform dot patterns over an area of 20 mm x 20 mm with the half pitch sizes of around 190, 250, and 370 nm are achieved and by increasing the beam power up to 0.600 mW/cm2, the exposure process time was reduced down to 12/12 sec for the positive photoresist DHK-BF424 (DongJin) over a bare silicon substrate. In addition, bottom anti-reflective coating (DUV-30J, Brewer Science) is applied to confirm improvements for line structures. The advantages and limitations of LIL are highlighted for generating nanoscale patterns.