Large-Area Nanoimprint Lithography and Applications

Large-area nanoimprint lithography (NIL) has been regarded as one of the most promising micro/nano-manufacturing technologies for mass production of large-area micro/nanoscale patterns and complex 3D structures and high aspect ratio features with low cost, high throughput, and high resolution. That opens the door and paves the way for many commercial applications not previously conceptualized or economically feasible. Great progresses in large-area nanoimprint lithography have been achieved in recent years. This chapter mainly presents a comprehensive review of recent advances in large-area NIL processes. Some promising solutions of large-area NIL and emerging methods, which can implement mass production of micro-and nanostructures over large areas on various substrates or surfaces, are described in detail. Moreover, numerous industrial-level applications and innovative products based on large-area NIL are also demonstrated. Finally, prospects, challenges, and future directions for industrial scale large-area NIL are addressed. An infrastructure of large-area nanoimprint lithography is proposed. In addition, some recent progresses and research activities in large-area NIL suitable for high volume manufacturing environments from our Labs are also introduced. This chapter may provide a reference and direction for the further explorations and studies of large-area micro/nanopatterning technologies

Nanoimprint lithography - the past, the present and the future

Background: Nanoimprinting lithography technique uses a very simple concept of transferring pattern of nanoscale features from a mold to a target substrate. In the past two decades, this technique has successfully broken through the barrier of laboratory scale production and become an industrial scale production technique. The aim of this paper is to introduce to readers to the basic working principle, applications, analysis the technological limitations. It will also point out future research direction of this useful nanofabrication technique. Methods: We adopted a systematic approach to give a comprehensive review of the work principle, hardware and analysis of advantaged and disadvantages of major nanoimprint lithography techniques. Moreover, a technical comparison of these methods is carried out to provide future research direction. Results: 87 papers were reviewed. Four techniques including thermal NIL, ultraviolet light NIL, laser-assisted direct imprint and nanoelectrode lithography have been identified as main stream of NIL techniques. These techniques possess certain advantages and disadvantages in terms of cost, throughput, attainable resolution. Lack of flexibility is the common limitation of current NIL techniques. NIL has gained wide applications in the fabrication of optoelectronics devices, solar cells, memory devices, nanoscale cells, hydrophobic surfaces and bio-sensors. The potential applications of NIL in biochips, artificial organs, diagnostic system, and fundamental research in cell biology will demand large scale 3D fabrication capability with resolution towards 10nm or less. Conclusions: The findings of this review confirm that NIL is one of the most employed commercial platforms for nanofabrication which offers high throughput and cost-effectiveness. One of the disadvantages of NIL over other nanofabrication techniques is the flexibility of patterning. Integrating NIL with other existing nanofabrication techniques can be helpful to overcome such issue. The potential applications of NIL in biochips, artificial organs, diagnostic system, and fundamental research in cell biology will attract researchers to push nanoimprint lithography forward at a resolution of 10 nm or less in the future

MICRO AND NANO R2R EMBOSSING OF EXTRUDED POLYMERS

This dissertation presents a process for directly imprinting or embossing extruded polymers as an advancement in roll-to-roll (R2R) embossing methods that avoids the problems of converting preformed films, increases throughput, and reduces costs. A proof-of-concept R2R apparatus was designed and constructed for directly embossing extruded polymer, and experimental results were evaluated. This laboratory scale R2R apparatus employed a thin metal ribbon belt mold with micro or nano scale features in a calendering setup, with a close coupled induction heating (IH) coil to preheat the ribbon mold above glass transition temperature (Tg) of the polymer, prior to contact with the extrudate at the nip of the calender. This allowed the melted polymer to fully fill the mold patterns before starting to solidify. The thin ribbon mold rapidly conducted heat to the calender roller, providing an effective cooling stage. Microscale and nanoscale features were imprinted directly onto extruded polymer film at a rate of 10 to 12 meters per second, three to over one hundred times the throughput of current R2R processes and orders of magnitude faster than planar processes. Metal ribbon mold belts with nano features were needed to test the direct embossing of extruded polymers at the nano scale. Three different avenues were taken to make such ribbon belts. First, preset nickel alloy molds were obtained. A master mold of the Book of Leviticus with letters 6 µm in width, 6 to 9 µm tall and 60-170 nm high and a nickel alloy DVD master mold with track pitch of 740 nm and 105 nm deep Pits between 400 nm and 1900 nm long. These were welded into stainless steel ribbon belts to form belt molds. Second, a process was developed using base forms or mandrels for metal-forming nickel ribbon belt molds with test patterns that included gratings from 70 to 500 nm and pillars having diameters of 1 µm, 700 nm, 500 nm and 350 nm. Third, an investigation of metal glass (MG) as a candidate mold material was undertaken and a laboratory scale mechanism was designed and constructed to emboss metal glass surfaced rollers thermally

NANOCHANNEL-ASSISTED ACTIVE CONTROL OF MASS TRANSPORT IN POLYDIMETHYLSILOXANE-BASED MICRO- /NANOFLUIDIC SYSTEMS

Department of Mechanical EngineeringNanofluidic devices have been extensively studied due to a fascinating nature of their small size which facilitates biosensing, bio-chemical separations, seawater desalination, nanofluidic transistors, protein, and preconcentration for a Lab-on-a-Chip (LOC). Such applications could be achieved by a control of electrokinetic transport in a nanochannel produced by sophisticated nanofabrication technique. However, it has been a challenge from a fabrication to the control of electrokinetic phenomena in nanochannel because of the cost, time, incompatibility, and addressability issues. Therefore, an innovative method is required to achieve simple fabrication and versatile operations of micro/nanofluidic device with limited resources. This dissertation proposes a new method for nanochannel-assisted active manipulation of mass transport by switching physicochemical environment. In the early chapters of this dissertation, unconventional fabrication methods for hybrid-scale micro-/nanofluidic devices is described by using both crack-photolithography and polydimethylsiloxane (PDMS) based soft lithography. The late chapters introduce the mechanism of the mass transport in micro/nanofluidic device using solutes gradient and humidity for manipulation of colloidal motion and molecule valves, respectively. These studies can be introduced as follows. First, crack-photolithography is employed to facilitate large-scale reproducible channel fabrication through a single molding process and thus enable the fabrication of hybrid-scale micro-/nanofluidic devices at a wafer level with advantages seen in the throughput, cost-effectiveness, reliability, and reproducibility. In addition, modified soft lithography process is developed to fabricate stable nanochannel which is free from the collapse and the crumbling. Second, crack-assisted nanochannel is introduced to manipulate physicochemical environment of neighboring microchamber. Diffusion-controlled ion transport produces solutes gradient inducing spontaneous electric field which affects the motion of colloidal particles. Since the single nanochannel allows the production of concentration gradient in a long-term and stable manner, least source is required to maintain the spontaneous electric field without any external power source, which is appropriate for a portable and self-containable LOC. As a practical application, integrated micro/nanofluidic device facilitates concentration, on-demand extraction, and separation of the colloidal particles. Third, gas permeable PDMS nanochannel with high hydraulic resistance is employed to develop humidity-based gating nanochannel. The rate of mass transport can be manipulated by humidity due to the evaporation of water and the adsorption of solutes to the wall of channel. To demonstrate functionality of humidity for liquid gating or capacitor of molecules, the effect of humidity on mass transport was investigated. This new concept of manipulation of nanofluidic transport made it possible to successfully perform individual mass transport control in a nanochannel array, which is difficult with conventional technique using electricity. It further facilitated on-demand addressable bio/chemical assay using humidity-based molecule valves and pumps. The role of nanochannel as a passage for mass transfer is essential to allow stable and precise control of transport of ions and molecules in the microchannel. It provides wide range of applications using a diffusion-based control of microfluidic environment to induce not only solute gradient for production of electric field but also liquid gating for a valve at molecular level. Thus, achievements of this dissertation contribute to raise the insight about nanochannel-assisted system for simple and precise control of mass transport in hybrid-scale micro-/nanofluidic devices, which is facilitated by the help of the cracking-assisted micro-/nanofabrication technologies.clos

Modeling multiphase flow and substrate deformation in nanoimprint manufacturing systems

Nanopatterns found in nature demonstrate that macroscopic properties of a surface are tied to its nano-scale structure. Tailoring the nanostructure allows those macroscopic surface properties to be engineered. However, a capability-gap in manufacturing technology inhibits mass-production of nanotechnologies based on simple, nanometer-scale surface patterns. This gap represents an opportunity for research and development of nanoimprint lithography (NIL) processes. NIL is a process for replicating patterns by imprinting a fluid layer with a solid, nano-patterned template, after which ultraviolet cure solidifies the fluid resulting in a nano-patterned surface. Although NIL has been demonstrated to replicate pattern features as small as 4 nm, there are significant challenges in using it to produce nanotechnology. Ink-jet deposition methods deliver the small fluid volumes necessary to produce the nanopattern, and drop volumes can be tuned to what the pattern requires. However the drops trap pockets of gas as they merge and fill the template, and due to relatively slow gas dissolution, reduce processing throughput. Capillary forces that arise from the gas-liquid interfaces drive non-uniform gap closure and the resulting variations in residual layer reduces process yield or degrades product performance. This thesis develops reduced-order models for fluid flow and structural mechanics of the imprint process for NIL. Understanding key phenomena of gas trapping and residual layer non-uniformity drives model development to better understand how throughput and yield can be improved. Reynolds lubrication theory, the \textit{disperse} type of multiphase flow, and a lumped-parameter model of dissolution unite to produce a two-phase flow model for NIL simulations of 10,000 drops per $\text{cm}^2$. Qualitative agreement between simulation and experiment provides a modicum of validation of this model for flow in NIL simulations. The two-phase model simulations predicts that both dissolution and viscous resistance affect throughput. The coupling of a reduced-order model for 3D structural mechanics with the two-phase flow model enables simulations of drop merger on a free-span tensioned web. Challenges in improving the structural model lead to formulation of a 2D model for which sources of instability are more easily discovered and understood. Inextensible cylindrical shell theory and lubrication theory combine into a model for the elastohydrodynamics of a rolling-imprint modality of NIL. Foil-bearing theory describes the lubrication layer that forms between a thin, tensioned web moving past another surface. Reproduction of the results of foil-bearing theory validates this coupled model and reveals a highly predictable region of uniformity that provides low shear stress conditions ideal for UV-cure. These results show theoretical limitations that are used to construct a processing window for predicting process feasibility

Stamp fabrication by step and stamp nanoprinting

The nanoimprinting is a potential method for submicron scale patterning for various applications, for example, electric, photonic and optical devices. The patterns are created by mechanical deformation of imprint resist using a patterned imprinting mold called also a stamp. The bottle-neck for imprint lithography is availability of the stamps with nanometer-scale features, which are typically fabricated by electron beam lithography. Therefore, patterning of a large stamp is time consuming and expensive. Nanoimprint lithography can offer a low cost and a high through-put method to replicate these imprinting molds. In this work, stamp replication process was developed and demonstrated for three different types of imprint molds. Replication relies on sequential patterning method called step and stamp nanoimprint lithography (SSIL). In this method a small master mold is used to pattern large areas sequentially. The fabricated stamps are hard stamps for thermal imprinting, bendable metal stamps for roll embossing and transparent stamps for UV-imprinting. Silicon is a material often used for fabrication of hard stamps for thermal imprinting. Fabrication process of silicon stamps was demonstrated using both the imprinted resist and lift-off process for pattern transfer into silicon. Bendable metal stamp for roll-to-roll application was fabricated using sequential imprinting to fabricate a polymer mold. The polymer mold was used for fabrication of a nickel copy in subsequent electroplating process. Thus fabricated metal stamp was used in a roll-to-roll imprinting process to transfer the patterns onto a CA film successfully. Polymer stamp for UV-imprinting was fabricated by patterning fluorinated polymer templates using sequential imprinting and a silicon stamp. The imprinted polymer stamp was used succesfully for UV-NIL. In the stamp fabrication process the features of the silicon stamp were replicated with good fidelity, retaining the original dimensions in all of three stamp types. The results shows, that the sequential imprinting is as a potential stamp replication method for various applications

ULTRAVIOLET ROLL-TO-ROLL NANOIMPRINT LITHOGRAPHIC FABRICATION OF FLEXIBLE POLYMER MOULDS

Ph.DDOCTOR OF PHILOSOPH

Modeling and controlling topographical nonuniformity in thermoplastic micro- and nano-embossing

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 221-236).The embossing of thermoplastic polymeric plates is valuable for manufacturing micro- and nanofluidic devices and diffractive optics. Meanwhile, the imprinting of sub-micrometer-thickness thermoplastic layers has emerged as a lithographic technique with exceptional resolution. Yet neither hot micro-embossing nor thermal nanoimprint lithography will be fully adopted without efficient numerical techniques for simulating these processes. This thesis contributes a computationally inexpensive approach to simulating the embossing of feature-rich patterns into thermoplastic polymeric materials. The simulation method employs a linear viscoelastic model for the embossed layer, and computes the distribution of contact pressure between the polymeric surface and an embossing stamp. An approximation to the embossed topography of the polymeric layer is thereby generated as a function of the material being embossed, the stamp's design, and the embossing process's temperature, duration, and applied load. For a stamp design described with an 800 x 800 matrix of topographical heights, simulation can be completed within 30-100 s using a computer with an Intel Pentium 4 processor and 2 GB RAM. This method is sufficiently fast for it to be employed iteratively when designing a pattern to be embossed or when selecting processing parameters. The method is able to build abstracted representations of feature-rich patterns, increasing the simulation speed still further. The viscoelastic properties of three materials - polymethylmethacrylate, polycarbonate, and Zeonor 1060R, a cyclic olefin polymer - have been experimentally calibrated as functions of temperature. For a test-pattern having features with diameters 5 [mu]m to 90 [mu]m, simulated and experimental topographies agree with r.m.s. errors of less than 2 [mu]m across all processing conditions tested, with absolute topographical heights ranging up to 30 [mu]m. In thermal nanoimprint lithography, the key challenge is to minimize spatial variation of the polymeric layer's residual thickness where stamp protrusions press down into the layer. The simulation method is therefore extended to incorporate elastic stamp deflections and their influence on residual layer thickness. Some design-rules are proposed that could help to minimize residual layer thickness variation. A way is also proposed for representing any shear-thinning of the imprinted layer.by Hayden Kingsley Taylor.Ph.D