Nanoimprint Lithography Molds Research Articles

3D ordered nanostructures fabricated by nanosphere lithography using an organometallic etch mask

A new approach for fabricating porous structures on silicon substrates and on polymer surfaces, using colloidal particle arrays with a polymer mask of a highly etch-resistant organometallic polymer, is demonstrated. Monolayers of silica particles, with diameters of 60 nm, 150 nm, 300 nm, or 500 nm, were deposited either on a silicon substrate or on a surface coated with polyethersulfone (PES), and the voids of the arrays were filled with poly(ferrocenylmethylphenylsilane) (PFMPS). Argon ion sputtering removed the excess PFMPS on the particles which enabled removal of the particles with HF. Further pattern transfer steps with reactive ion etching for different time intervals provided structures in silicon or in a PES layer. Free-standing PES membranes exhibiting regular arrays of circular holes with high porosity were fabricated by using cellulose acetate as a sacrificial layer. The pores obtained on silicon substrates after etching were used as molds for nanoimprint lithography (NIL). A combination of the techniques of nanosphere lithography (NSL) and NIL has resulted in 3D nanostructures with a hemispherical shape (inherited from the nanoparticles) which was obtained both in silicon and in PMMA.

Molecular dynamics study on compressive strength of monocrystalline, nanocrystalline and amorphous Si mold for nanoimprint lithography

Molecular dynamics studies are carried out to investigate the compressive strengths and the failure mechanisms of monocrystalline, nanocrystalline and amorphous Si molds for nanoimprint lithography. The stress–strain characteristics and the stress distributions are analyzed for the three types of Si molds. The stress–strain characteristics show that the strength of the monocrystalline Si mold is the greatest among the three types of Si molds. The strength of the nanocrystalline Si mold decreases as the grain size decreases. This shows the Hall–Petch effect does not hold true in the grain size of nanometer order. The visualization of the stress distribution shows that the monocrystalline, nanocrystalline and amorphous Si mold fail due to the slipping of the specific atomic plane, the sliding in the grain boundaries and the nonlocal plastic deformation, respectively. As a result, the monocrystalline Si mold is the most suitable for nanoimprint lithography among the three types of Si molds in the nanoscale regime.

Replica Mold for Nanoimprint Lithography from a Novel Hybrid Resin

The use of durable replica molds with high feature resolution has been proposed as an inexpensive and convenient route for manufacturing nanostructured materials. A simple and fast duplication method, involving the use of a master mold to create durable polymer replicas as imprinting molds, has been demonstrated using both UV- and thermal nanoimprinting lithography (NIL). To obtain a high-durability replicating material, a dual UV/thermal-curable, organic-inorganic hybrid resin was synthesized using a sol-gel-based combinatorial method. The cross-linked hybrid resin exhibited high transparency to UV light and resistance to organic solvents. Molds made of this material showed good mechanical properties (Young's modulus=1.76 GPa) and gas permeability. The low viscosity of the hybrid resin (approximately 29 cP) allowed it to be easily transferred to relief nanostructures on transparent glass substrates using UV-NIL at room temperature and low pressure (0.2 MPa) over a relatively short time (80 s). A low surface energy release agent was successfully coated onto the hybrid mold surface without destroying the imprinted nanostructures, even after O2 plasma treatment. Nanostructures with feature sizes down to 80 nm were successfully reproduced using these molds in both UV- and thermal-NIL processes. After repeating 10 imprinting cycles at relatively high temperature and pressure, no detectable collapse or contamination of the replica surface was observed. These results indicate that the hybrid molds could tolerate repeated UV- and thermal-NIL processes.

Characteristics of Antisticking Layer Formed by CHF3 Plasma Irradiation for Nanoimprint Molds

Nanoimprint lithography (NIL) is very useful for mass-producing nanostructure devices at a low cost and a high throughput. To avoid the adhesion of replication materials, NIL molds are usually coated with an antisticking fluorinated self-assembled monolayer. In this study, we used a fluorinated plasma chemical vapor deposition film as the antisticking layer. First, we formed a CHF3 plasma chemical vapor deposition (CVD) film on SiO2/Si and quartz molds and carried out thermal and UV nanoimprint using these molds. However, the film was removed from these molds. We found that the proposed method can solve this problem. We irradiated plasma using a gas mixture of CHF3 and O2 as the source gas onto SiO2/Si and quartz molds. As imprinting results, the patterns were successfully imprinted onto the resins without the removal of the plasma CVD film. In addition, we were able to carry out 100 times of repeated nanoimprinting using the plasma-CVD-film-coated SiO2/Si mold.

Plasma fluorination of diamond-like carbon surfaces: mechanism and application tonanoimprint lithography

Diamond-like carbon (DLC) films, used as molds for nanoimprint lithography, weretreated with a fluorocarbon-based plasma in order to enhance their anti-adhesionproperties. While ellipsometry and atomic force microscope measurementsshowed negligible changes in thickness and surface roughness after plasmaprocessing, contact angle measurement found fluorine plasma-treated DLCsurfaces to be highly hydrophobic, with surface energy values reduced from∼45 mJ m−2 for untreatedfilms to ∼20–30 mJ m−2 after fluorination. X-ray photoelectron spectroscopy revealed a thin (from∼0.5 to∼3 nm) fluorocarbon layer on the DLC surface. Proposed mechanisms for the formation ofthis layer include two competing processes: etching of DLC and deposition offluorocarbon material, with one or the other mechanism dominant, depending on theplasma conditions. Fluorocarbon plasma-treated DLC molds for nanoimprintlithography were used to pattern sub-20 nm size features with a high degree ofrepeatability, demonstrating an extended lifetime of the anti-adhesion coating.

Nanoimprint mold fabrication and duplication for embedded servo and discrete track recording media

A master mold for nanoimprint lithography was fabricated for discrete track recording (DTR) media using electron beam lithography and conventional etching techniques. The DTR pattern, containing 167 tracks of 120 nm pitch (60 nm land and groove widths) and embedded servo information, was automatically generated using an in-house developed program and was optimized for faster electron beam writing on an x-y stage. A daughter mold was duplicated from the master mold by nanoimprinting, using UV-curable resist and an intermediate polymer stamp technique. Scanning electron microscope images showed that the daughter mold was accurately and completely reproduced from the master mold.

Design of Ni Mold for Discrete Track Media

Nano imprint lithography (NIL) and NIL mold formation play a vital role in discrete track media (DTM) production. In this paper, we created a nickel (Ni) mold for DTM production using an R-theta electron beam mastering device to draw data groove and servo information on a silicon substrate master, and transferred the resulting pattern to a nickel mold via an electroplating process. The resulting Ni mold exhibits a 90-nm track pitch (282 kTPI equivalent), 30-nm line width, 60-nm groove width, 60-nm land height, and 7-nm line width roughness (LWR). Since variations in downtrack LWR and line edge roughness (LER) on the Ni mold are much smaller than variations in the size of HDD media magnetic clusters, we believe the Ni mold production method that is the subject of this study can be successfully applied to the production of DTM molds for next-generation HDD media.

Nanoimprint lithography patterns with a vertically aligned nanoscale tubular carbonstructure

A nanoscale tubular carbon structure array was demonstrated as a mold for nanoimprintlithography (NIL), in which a vertically formed and hexagonally aligned nanoscale tubularcarbon array was fabricated through carbon growth inside an anodic aluminum oxide (AAO)nanotemplate, followed by controlled chemical etching of the AAO layer. High density (over1010 cm−2) of the nanoscale carbon pillars with their controlled diameters and protruded lengths wasinversely replicated onto a UV-curable resist for the first time using the imprintinglithography technique.

Molecular Dynamics Study of Yield Stress of Si Mold for Nanoimprint Lithography

Molecular dynamics studies are carried out to investigate the fracture mechanism of a crystalline Si mold for nanoimprint lithography (NIL). The stress–strain characteristics are evaluated for mold models with various crystalline orientations, and temperature effects on strength are calculated. It is found that the behavior of the fracture and the yield stress of the mold are strongly associated with the configurations of the {111} planes in the mold. The simulation results indicate that crystals with a {100} top surface are more suitable for a mold with arbitrary patterns than those with a {110} top surface because of the weaker dependence of yield stress on crystalline orientation.

Achieving High Aspect Ratio of Track Length to Width in Molds for Discrete Track Recording Media

Discrete track media (DTM) fabricated by nanoimprint lithography (NIL) is considered as a potential technology for future hard disk drives (HDD). In the fabrication of a master mold for NIL, patterning the resist tracks with a narrow distribution in the width is the first critical step. This paper reports the challenges involved in the fabrication of high aspect ratio discrete tracks on Polymethylmethacrylate (PMMA) resist by means of electron beam lithography. It was observed that fabrication parameters applied for successful patterning of discrete tracks in nanoscale length were not directly suitable for the patterning of discrete tracks in micron scale. Hence different approaches such as thick layer resist coating, introducing of post exposure baking process, and varying of exposure parameters were used in order to achieve uniform sharp discrete tracks in micron scale length on the resist. The optimal parameters were used to pattern 20 μm long tracks with 70 nm track pitch on the resist.

Fabrication of three dimensional structures for an UV curable nanoimprint lithography mold using variable dose control with critical-energy electron beam exposure

In three dimensional (3D) printing the most challenging aspect is in the mold making process. The authors have developed a process for making 3D structures in a simple two-step process. The 3D profiles are created on a negative tone photoresist using electron beam lithography with variable dose and critical-energy electron beam exposure. Resist contrast profiles have been obtained with a negative tone photoresist from Microresist (ma-N2403) and subsequently have been utilized as the 3D masking layer. The 3D patterns have been transferred into a quartz mold by single-step reactive ion etching (RIE) with suitable resist-to-substrate selectivity. The precision of the fabricated structures is important, especially for micro-optic devices. Surface roughness below 2nm has been achieved when the RIE process pressure is lower than 6mTorr. The differences between intended and final dimensions are also analyzed. By employing this technique, complex structures for 3D quartz molds can be fabricated with simplified steps.

A poly(dimethylsiloxane)-coated flexible mold for nanoimprint lithography

In this paper, we introduce an anti-adhesion poly(dimethylsiloxane) (PDMS)-coatedflexible mold and its applications for room-temperature imprint lithography. The flexiblemold is fabricated using an ultraviolet-curable prepolymer on a flexible substrate, and itssurface is passivated with a thin layer of PDMS to impart an anti-adhesion property. Thehighly flexible mold enables conformal contact with a substrate on which a low-viscositypolymer resist is spin-cast in a thin layer. Large-area imprinting is then realized at roomtemperature under significantly reduced pressure. The mold was durable even afterrepetitive imprinting of over 200 times. Also, we show a double imprinting on the substratewith a PDMS-coated replica polymeric mold having 500 nm line patterns. This enablesthe formation of matrix patterns with varying feature heights in less than 7 min.

Nanoimprint mold fabrication and replication by room-temperature conformal chemical vapor deposition

The authors present a technique for the replication of molds for nanoimprint lithography (NIL) without solvents or etching. A thin hard amorphous silicon film is deposited onto imprinted or self-assembled polymer nanostructures by room-temperature conformal plasma-enhanced chemical vapor deposition. After attachment to another substrate and separation from the polymer original, the thin hard film forms a NIL mold that is the inverse of the polymer original. Using this technology, the authors demonstrate the replication of a 200nm pitch grating mold and sub-50-nm features over wafer-scale areas without introducing additional line edge roughness associated with conventional replication methods.

Large area 50nm period grating by multiple nanoimprint lithography and spatial frequency doubling

The authors have developed an approach to fabricate large area 50nm period gratings (22nm linewidth) with low cost. The method used a fabrication cycle twice, each combining nanoimprint lithography with a spatial frequency doubling based on electroless plating, lift-off, and reactive ion etching. Hence by frequency doubling twice, we started with a 200nm period grating mold and finished with a 50nm period grating with a uniform area of 3cm2—the largest achieved today. This method is scalable for the fabrication of even smaller period gratings over a large area, and is a viable low-cost technique for making nanoimprint lithography molds for high-throughput fabrication of 50nm period grating or grid devices.

Vertically Aligned Nanopillar Arrays with Hard Skins Using Anodic Aluminum Oxide for Nano Imprint Lithography

Master molds with nano-pillar structures were fabricated by using anodic aluminum oxide (AAO) for nano-imprint lithography (NIL). The proposed method consists of (1) AAO fabrication, (2) transfer of the thin AAO layer onto a substrate, (3) aluminum sputtering, (4) aluminum melting, and (5) removal of the thin AAO layer. Since the sputtered aluminum penetrated into the porous alumina walls of the AAO template during the melting step, the pillars had skin layers of aluminum/alumina composite which added additional mechanical strength and chemical resistance. The diameter of a pillar in the nano-pillar master mold was larger than that of the hole diameter of the original AAO template because of the hard skin of aluminum/alumina composite layer which covers the pillar surface. The pillar structure could be used as a mold for NIL, resulting in a regular pore array on a polymer film.

Cross-linked Polymer Replica of a Nanoimprint Mold at 30 nm Half-pitch

This letter reports the demonstration of a photocurable polymer process for replicating the master mold for nanoimprint lithography. The cross-linked polymer mold was fabricated directly with high fidelity from a master by imprinting and photocuring a low viscosity liquid prepolymer film spun onto a substrate. The surface of the cross-linked polymer mold can be treated using an O(2) plasma, and then vapor primed with a low surface energy mold release layer for repeatable imprinting. The imprinting results demonstrated that the cross-linked polymer mold could be faithfully used for both thermal and photocurable nanoimprint lithography.

Rigid organic molds for nanoimprint lithography by replica molding of high glass transition temperature polymers

The glass transition of polycarbonate resins of high softness temperature is exploited to realize rigid polymeric replicas of master patterns, with no need for antisticking layers and applied pressure. Such replicas enable the transfer of patterns onto polymers having a lower glass-transition temperature by nanoimprint lithography. As a demonstration, we show the pattern transfer onto poly(methylmethacrylate), which demonstrates good fidelity and remarkable simplicity of the process.

One-step lithography for various size patterns with a hybrid mask-mold

Nanoimprint lithography (NIL) has been successfully employed in nanoscale patterning, however, it is known to have limitations in replicating large-scale (hundreds of microns and larger) and nanoscale patterns simultaneously. In this letter, we present a novel lithographic technique that integrates photolithography into the NIL patterning process. This technique uses a hybrid mask-mold that has large metal pads embedded in a transparent NIL mold. Such a hybrid mold allows both large- and nanoscale patterns to be replicated in one step by a combination of imprinting and photolithography. In addition, this new technique offers the advantages of simplifying residual layer distribution and avoiding NIL failures resulting from insufficient polymer flow.

Fabrication of multiple nano-electrodes for molecular addressing using high-resolution electron beam lithography and their replication using soft imprint lithography

Abstract We investigate the ability for High Resolution Electron Beam Lithography (HREBL) to fabricate multiple nano-electrodes with the smallest gap in the smallest area. By using both standard PolyMethylMethAcrylate (PMMA) as resist and standard MIBK/IPA development, we show that up to 10 nano-electrodes can be realized in an area as small as 65 nm. The obtained structures have been used either for the realization of embedded electrodes in SiO 2 by wet etching followed by lift-off, or for the fabrication of molds for Nano-Imprint Lithography using PMMA as a mask for Reactive Ion Etching of silicon. Preliminary results on the replication of these molds using a soft nano-imprint process are also presented.

Direct three-dimensional patterning using nanoimprint lithography

We demonstrated that nanoimprint lithography (NIL) can create three-dimensional patterns, sub-40 nm T-gates, and air-bridge structures, in a single step imprint in polymer and metal by lift-off. A method based on electron beam lithography and reactive ion etching was developed to fabricate NIL molds with three-dimensional protrusions. The low-cost and high-throughput nanoimprint lithography for three-dimensional nanostructures has many significant applications such as monolithic microwave integrated circuits and nanoelectromechanical system.