Soft UV Nanoimprint Lithography Research Articles

Patterned self-assembly of gold nanoparticles on chemical templates fabricated by soft UVnanoimprint lithography

Chemical templates for the patterned immobilization of gold nanoparticles were fabricatedby soft UV nanoimprint lithography. The template structures were fabricated by means ofthe consecutively performed process steps of nanoimprint lithography, reactive ion etching,chemical functionalization with amino groups, and lift-off of imprint resist. These chemicaltemplates were used for the defined assembly of 20 nm diameter citrate stabilizedgold nanoparticles from aqueous solution. By reducing the ionic strength of thesolution, one- and zero-dimensional particle assemblies were generated on sub-100-nmtemplate structures. By this means, the pattern resolution predefined by thelithography process could be easily enhanced by dilution of the nanoparticle solution.

Microcontact printing of biomolecular gratings from SU-8 masters duplicated by Thermal Soft UV NIL

Thermal Soft UV nanoimprint lithography (NIL) was performed to replicate nanostructures in SU-8 resist. The SU-8 resist was structured with a PDMS stamp molded against an original silicon master which comported gratings of lines (500nm width/1μm pitch). The patterns obtained in SU-8 were used in a second step as a template for PDMS molding of daughter stamps. Pattern transfer quality and dimension control were achieved on these second generation PDMS stamps using AFM measurements. As a final validation of the whole duplication processes, these second generation PDMS stamps were finally employed to perform μCP of streptavidin molecules on a glass slide activated by plasma O2 treatment. AFM observation and fluorescence microscopy reveal that molecular patterns produced with SU8-molded PDMS stamps are not discernable from those obtained with a PDMS stamp directly molded on the original silicon master. Coupling Thermal Soft UV NIL and microcontact printing opens a new method for generating a large quantity of SU-8 templates on which functional PDMS stamps can be replicated in a reduced time. We thus propose a functional duplication process for soft-lithography implementation which may further reduce the cost of this technology for industrial development.

Nanoimprint lithography patterned GaAs templates for site-controlled InAs quantum dots

We report on the development of a soft UV-nanoimprint lithography (UV-NIL) based process to fabricate nanopatterned templates for epitaxy of site-controlled Stranski–Krastanov grown quantum dots. Surface cleaning and chemical native oxide removal processes are analyzed in detail. The quality of the surface is studied by means of scanning electron microscopy, atomic force microscopy and photoluminescence analysis. To evaluate the suitability of the process for fabricating high optical quality site-controlled quantum dots, we have investigated the photoluminescence signal of the near-surface quantum well and overgrown quantum dots. We present the successful growth of optically active, site-controlled InAs quantum dots, both in the ensemble and single-dot regime, by molecular beam epitaxy on UV-NIL patterned GaAs surfaces using only chemical cleaning prior to the growth.

Deformation of nanostructures on polymer molds during soft UV nanoimprintlithography

Soft nanoimprint lithography (soft NIL) relies on a mechanical deformation of a resist by apatterned polymer used as a mold. Here, we report on the investigation of the nanopatternfidelity of the high pressure imprint process based on a perfluorinated polyether (PFPE)soft mold material. The perfluorinated polyether material was found to be well suited totransfer the mold pattern into the resist by a direct imprinting process at low cost.Moderate deformations of the polymer mold structures occurring during the high pressureimprint are systematically studied. Features of decreased size are found to be moresensitive to pattern distortions. An optimized pattern design with increased structuredensity and constant pattern ratio is developed to minimize deformation effects.Imprints performed on the basis of these design rules result in reduced deformationsand repeal their size dependence. The improved pattern transfer, especially forsmall structural elements, turns the direct and cost-effective soft UV-NIL into aninteresting technique also for patterning tasks in the lower nanometer range.

Enhanced efficiency of light emitting diodes with a nano-patterned gallium nitride surfacerealized by soft UV nanoimprint lithography

This paper reports a significant enhancement in the extraction efficiency of nano-patternedGaN light emitting diodes (LED) realized by soft UV nanoimprint lithography. The 2 inchsoft stamp was fabricated using a replication stamp of anodic alumina oxide (AAO)membrane. The light output power was enhanced by 10.9% compared to that of the LEDsample without a nano-patterned surface. Up to 41% enhancement in photoluminescenceintensity was obtained from the nano-patterned GaN LED sample. The method is simple,cheap and suitable for mass production.

Sub-200nm gap electrodes by soft UV nanoimprint lithography using polydimethylsiloxane mold without external pressure

In this article, the authors present an alternative approach to electron beam lithography allowing the fabrication of gap electrodes with dimensions less than 200nm. This approach consists of the soft ultraviolet nanoimprint lithography on nonstandard sample sizes, using polydimethylsiloxane (PDMS) as a flexible mold material. By simple deposit of the PDMS mold on the substrate, they succeeded in imprinting gaps in Amonil and the transfer of patterns of polymethylmethacrylate/Amonil bilayer was achieved by etching the substrate with a suitable reactive ion etching process. The imprint pressure was ensured by only the weight of the PDMS mold.

High resolution and hybrid patterning for single cell attachment

We present a method to fabricate topographical and chemical patterns for cell attachment studies. Soft UV nanoimprint lithography, photolithography and reactive ion etch techniques are combined to produce high resolution line-and-space grating arrays on a quartz plate. Then, micro-contact printing is used to add protein patterns on the topographic features to promote cell adhesion on selected areas. We found that the hybrid patterns with a dimension comparable to the size of cells have pronounced effects on the cell adhesion and its morphological changes.

A versatile pattern inversion process based on thermal and soft UV nanoimprint lithography techniques

Si master molds are generally patterned by electron-beam lithography (EBL) that is known to be a time-consuming nanopatterning technique. Thus, developing mold duplication process based on high throughput technique such as nanoimprint lithography can be helpful in reducing its fabrication time and cost. Moreover, it could be of interest to get inverted patterns (holes instead of pillars) without changing the master EBL process. In this paper, we propose a two step process based on thermal nanoimprint lithography (T-NIL) (step 1) and soft UV assisted nanoimprint lithography (UV-NIL) (step 2) to invert a master EBL mold. After the two inversion steps, the grand-daughter Si mold exhibits the same pattern polarity as the EBL mold. For step 1, pattern transfer using ion beam etching (IBE) of a thin metallic underlayer is the critical step for dimension control due to the low NXR1020 resistance. For step 2, the optimized reactive ion etching (RIE) step allows transfer with good anisotropy even for nanostructures at the 50 nm-scale. For structures larger than 100 nm, this inversion process has been successfully applied to large field replication (up to 1.5 cm 2) on whole wafer.

Gold nanoparticles by soft UV nanoimprint lithography coupled to a lift-off process for plasmonic sensing of antibodies

In this paper, we present the results of gold nanoparticles fabrication on large area by soft UV nanoimprint lithography (UV-NIL) and lift-off process for antibodies sensing. For this fabrication, the hard polydimethylsiloxane (H-PDMS) is used as flexible mold material. A simple AMONIL/PMMA bilayer is used to transfer patterns by etching the substrate with a suitable RIE process. The UV-NIL process has enabled to obtain gold nanoparticles with a diameter about 160 nm on a zone of 1 mm 2. For bioplasmonic applications, the sensing of Anti-Biotin was studied.

Gold nanohole arrays for biochemical sensing fabricated by soft UV nanoimprint lithography

We report on results of fabrication and optical characterisation of sub-250 nm periodic gold nanohole arrays on glass by using UV nanoimprint lithography (UV-NIL) combined with both reactive ion etching (RIE) and Cr/Au lift-off processes. The transmission spectra of the fabricated nanohole gratings were measured for different hole diameters and periods. We also show preliminary results of chemical sensing after surface modification of the gold hole arrays. In agreement with the theoretical prediction, we found that any change in the dielectric index of the surrounding environment of the metallic array produces a transmission peak red shift.

Nanoholes by soft UV nanoimprint lithography applied to study of membrane proteins

In this paper, we present an alternative technique to the well-known electron beam lithography in order to realize nanoholes in the silicon substrates for biological applications. The used technique is soft UV nanoimprint lithography (UV-NIL). We optimized the fabrication of silicon based supports obtained by soft UV-NIL and reactive ion etching to carry out very large arrays of nanoholes. The resolution limits are investigated when using poly(dimethylsiloxane) as flexible mold material. RIE conditions are initiated to limit the lateral mask resist etch.

Fabrication of metallic nanocavities by soft UV nanoimprint lithography

We propose a process combining UV-assisted nanoimprint lithography (NIL) and shadow mask evaporation techniques to fabricate metallic nanoparticles with cavities. A bi-layer transparent soft stamp with a hard top layer containing the high resolution patterns was obtained by spin coating and casting methods of PDMS. Then, it was used to mold the top photo-curable resist on a thick PMMA layer. After removal of the residual NIL resist layer, high density and high aspect ratio PMMA nanopillar arrays were obtained by reactive ion etching. Afterward, a four step evaporation under oblique angle was performed to deposit the gold nanostructures at the top of nanopillars. After lift-off, uniformly sized gold nanocavities were collected. Dark-field microscopy imaging of the fabricated nanocavities shows a clear geometry dependence of the emission peak wavelength, thereby providing a novel types of bio-sensing nano-objects.

Applications of UV-nanoimprint soft stamps in fabrication of single-frequency diode lasers

We show how to use a modified poly-dimethyl-siloxane (PDMS) soft stamp to reduce pattern deformation and residual layer thickness in soft UV-nanoimprint lithography. A soft stamp thinned with toluene reduces the residual layer of a resist by as much as 50% compared to an unthinned stamp. We apply the soft UV-nanoimprint to prepare nanopatterned waveguides for a single-frequency diode laser. This laser operates with a side-mode suppression ratio of 50 dB, which indicates that the patterns are precise and uniform over the whole imprint field. To the best of our knowledge, this is the first single-frequency laser fabricated by soft UV-nanoimprint technology.

Mold deformation in soft UV-nanoimprint lithography

UV-nanoimprint lithography (UV-NIL) using a soft mold is a promising technique with low cost and high throughput for producing the submicron scale large-area patterns. However, the deformations of the soft mold during imprinting process which can cause serious consequences have to be understood for the practical application of the process. This paper investigated the deformation of the soft mold by theoretical analyses, numerical simulations, and experimental studies. We simulated the mold deformation using a simplified model and finite element method. The simulation and the related experimental results agree well with each other. Through the investigation, the mechanism and affected factors of the mold deformation are revealed, and some useful conclusions have been achieved. These results will be valuable in optimizing the imprinting process conditions and mold design for improving the quality of transferred patterns.

Patterning Biomolecules with a Water-Soluble Release and Protection Interlayer

We report on a general lithography method for high-resolution biomolecule patterning with a bilayer resist system. Biomolecules are first immobilized on the surface of a substrate and covered by a release-and-protection interlayer of water-soluble polymer. Patterns can then be obtained by lithography with a spin-coated resist layer in a conventional way and transferred onto the substrate by reactive ion etching. Afterward, the resist layer is removed by dissolution in water. To demonstrate a high-resolution patterning, soft UV nanoimprint lithography has been used to produce high-density dot arrays of poly-(L-lysine) molecules on a glass substrate. Both fluorescence images and cell proliferation behaviors on such a patterned substrate have shown evidence of improved stability of biomolecule immobilization comparing to that obtained by microcontact printing techniques.

Highly parallel mix-and-match fabrication of nanopillar arrays integrated in microfluidic channels for long DNA molecule separation

We report on a mix-and-match method based on a combination of soft UV nanoimprint lithography, contact optical lithography, and reactive-ion-etch techniques, which is applicable for high throughput manufacturing of nanostructure integrated microfluidic devices. We demonstrate the integration of high density and high aspect ratio nanopillars into microfluidic channels as electrophoresis sieving matrices. As a result, λ DNA and T4 DNA can be separated within a few minutes. By changing the pattern design, the device could be used for separation of other types of molecules.

Fabrication and surface functionalization of high aspect ratio plastic nanostructures

Soft UV nanoimprint lithography and reactive ion etch techniques have been used to pattern high density and high aspect ratio nanostructures on the surface of a plastic plate such as Plexiglas. A thin film of photo-curable resist is first spin coated on the plastic plate, with or without deposition of a 10 nm thick germanium intermediate layer. Then, a soft stamp made of poly-dimethylsiloxane (PDMS) is used to mold the photo-curable resist, followed by a UV light exposure. Finally, the imprinted pattern is used as mask for a sequential reactive ion etch of the residual resist layer, the intermediate layer if any, and the plastic plate. Such a soft nanoimprint and direct etch technique allowed us to obtain high density nanostructures with an aspect ratio up to 15. To demonstrate the applicability of such systems in biology, wetting behaviours and surface functionalization with fluorescent protein molecules have been studied. We believe that this low cost approach is high throughput and efficient for a number of applications.

Fabrication of integrated patterns using lithography and particles assembling techniques

This paper describes both physical and chemical techniques of nanoparticle assembling on a substrate pre-patterned by optical lithography or soft UV nanoimprint lithography. Integrated patterns of mono dispersed particles can be achieved by capillary forces, whereas functionalized particles could be assembled into holes of a metallic layer by chemical processing. To demonstrate the applicability of the methods, the fabricated patterns were transferred into a UV curable resist or a silicon dioxide layer by reactive ion etching. In addition, particles assembled into a microfluidic channel were used as artificial gel to show the feasibility of stretching single-strand T4 DNA molecules.

Improved mold fabrication for the definition of high quality nanopatterns by Soft UV-Nanoimprint lithography using diluted PDMS material

An improved mold fabrication process that utilizes toluene diluted polydimethylsiloxane (PDMS) as flexible mold material was developed. Various toluene concentrations and their implication on the pattern definition using the Soft UV-Nanoimprint process were analyzed and discussed. Dots with a resolution of 50 nm are well replicated and an excellent imprint homogeneity across a 4 in. wafer with one imprint step only is demonstrated.

Fabrication of SOI photonic crystal slabs by soft UV-nanoimprint lithography

Soft imprinting lithography assisted by UV light (soft UV-NIL) takes advantage of both, UV-nanoimprint and soft lithography. This technique, which can be applied for the replication of nanometer size features over large areas, is suitable for the patterning of nanostructures like photonic crystals with high throughput and high accuracy. In this work, we demonstrate the fabrication of two dimensional silicon-on-insulator photonic crystal slabs with and without line defects by using soft UV-NIL. Measurement of photonic mode dispersion by means of variable angle reflectance assesses the quality of the fabricated samples.