Nanoimprint lithography (NIL) is a nonconventional lithographic technique for high-throughput patterning of polymer nanostructures at great precision and at low costs. Unlike traditional lithographic approaches, which achieve pattern definition through the use of photons or electrons to modify the chemical and physical properties of the resist, NIL relies on direct mechanical deformation of the resist material and can therefore achieve resolutions beyond the limitations set by light diffraction or beam scattering that are encountered in conventional techniques. This Review covers the basic principles of nanoimprinting, with an emphasis on the requirements on materials for the imprinting mold, surface properties, and resist materials for successful and reliable nanostructure replication.

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Nanoimprint Lithography: Methods and Material Requirements**

A versatile "top-down" method for the fabrication of particles, Particle Replication In Nonwetting Templates (PRINT), is described which affords absolute control over particle size, shape, and composition. This technique is versatile and general enough to fabricate particles with a variety of chemical structures, yet delicate enough to be compatible with sophisticated biological agents. Using PRINT, we have fabricated monodisperse particles of poly(ethylene glycol diacrylate), triacrylate resin, poly(lactic acid), and poly(pyrrole). Monodisperse particle populations, ranging from sub-200 nm nanoparticles to complex micron-scale objects, have been fabricated and harvested. PRINT uses low-surface energy, chemically resistant fluoropolymers as molding materials, which eliminates the formation of a residual interconnecting film between molded objects. Until now, the presence of this film has largely prevented particle fabrication using soft lithography. Importantly, we have demonstrated that PRINT affords the simple, straightforward encapsulation of a variety of important bioactive agents, including proteins, DNA, and small-molecule therapeutics, which indicates that PRINT can be used to fabricate next-generation particulate drug-delivery agents.

Direct Fabrication and Harvesting of Monodisperse, Shape-Specific Nanobiomaterials

Nanoimprint is an emerging lithographic technology that promises high-throughput patterning of nanostructures. Based on the mechanical embossing principle, nanoimprint technique can achieve pattern resolutions beyond the limitations set by the light diffractions or beam scatterings in other conventional techniques. This article reviews the basic principles of nanoimprint technology and some of the recent progress in this field. It also explores a few alternative approaches that are related to nanoimprint as well as additive approaches for patterning polymer structures. Nanoimprint technology can not only create resist patterns as in lithography but can also imprint functional device structures in polymers. This property is exploited in several non-traditional microelectronic applications in the areas of photonics and biotechnology.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/48920/d4_11_r01.pdf?sequence=2

Recent progress in nanoimprint technology and its applications

Advances in top-down and bottom-up surface nanofabrication: techniques, applications & future prospects.

We report advances in nanoimprint lithography, its application in nanogap metal contacts, and related fabrication yield. We have demonstrated 5nm linewidth and 14nm linepitch in resist using nanoimprint lithography at room temperature with a pressure less than 15psi. We fabricated gold contacts (for the application of single macromolecule devices) with 5nm separation by nanoimprint in resist and lift-off of metal. Finally, the uniformity and manufacturability of nanoimprint over a 4in. wafer were demonstrated.

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Fabrication of 5 nm linewidth and 14 nm pitch features by nanoimprint lithography

We have finished the construction of an automated tool for step and flash imprint lithography. The tool was constructed to allow defect studies by making multiple imprints on a 200 mm wafer. The imprint templates for this study were treated with a low surface energy, self-assembled monolayer to ensure selective release at the template-etch barrier interface. This surface treatment is very durable and survives repeated imprints and multiple aggressive physical and chemical cleanings. The imprint and release forces were measured for a number of successive imprints, and did not change significantly. The process appears to be “self-cleaning.” Contamination on the template is entrained in the polymerizing liquid, and the number of defects is reduced with repeated imprints.

http://willson.cm.utexas.edu/research/sub_files/sfil/publications/2000/bailey et al jvstb nov 2000.pdf

Step and flash imprint lithography: Template surface treatment and defect analysis

Step and flash imprint lithography (SFIL) is a promising, low cost alternative to projection printing. This technique has demonstrated very high resolution and overlay alignment capabilities, but it is a contact printing technique so there is concern about defect generation and propagation. A series of experiments has been carried out with the goal of quantifying the effect of defect propagation. To that end, each unit process in SFIL was studied independently. The number of particles added during handling and transportation and due to SFIL machinery was deemed acceptable, and the added particles should not complicate the inspection of process defects. The concept of a “self-cleaning” process in which the imprint template becomes cleaner by imprinting was revisited. Inspection of an imprint template before and after imprinting revealed that the template actually becomes cleaner with imprinting. Visual inspection of multiple imprints did not reveal any systematic generation or propagation of defects. The inspection area used in this study was limited, however, since the inspection was both manual and visual. Imprinting for this defect study was performed at the University of Texas in a Class 10 cleanroom, and inspection was performed at International SEMATECH.

Step and flash imprint lithography: Defect analysis

Template fabrication schemes for step and flash imprint lithography

The development of imprint lithography is an attempt by researchers to meet or exceed the size targets outlined in the SIA roadmap for semiconductors, while circumventing the expensive exposure sources and optics required by more conventional next generation lithographies, such as extreme UV, electron projection, and X-ray lithographies. There are promising applications in addition to the semiconductor arena, such as micro-electromechanical devices (MEMs), micro-optics, and patterned storage media. Imprint lithography has the advantage that it uses fundamental fluid displacement principles to define a pattern, rather than i mage reduction with diffraction corrections, but the temperatures required by the more traditional micromolding or hot embossing techniques may present insurmountable obstacles in overlay alignment accuracy, and for applications requiring high throughput. Step and Flash Imprint Lithography (SFIL), being developed primarily at the University of Texas at Austin, overcomes these issues by using a rigid, UV-transparent imprint template, and a bilayer resist scheme composed of an organic planarizing layer and a low viscosity, UV-curable organosilicon solution for imprint imaging. We describe the technology fundamentals here. We demonstrate a durable, low surface energy template release coating, a UV-curable organosilicon etch barrier that cures with low dosage, and the equipment that allows for the high-precision orientation of the template/substrate system necessary for imprint patterning. We have demonstrated printed features as small as 60 nm (not shown), compatibility with metal lift-off processing, functional optical devices including a micropolarizer array, and the ability to pattern high-aspect ratio, sub 0.25 micron features over a non-flat substrate.

/pdf/step-and-flash-imprint-lithography-a-technology-review-2ec33r1dr8.pdf

Step and Flash Imprint Lithography: A Technology Review

Semiconductor wafer nanolithography machines integrate nano-scale precision mechanisms with advanced optical and mechatronic modules to achieve highly controlled nanopatterning capability for fabricating advanced integrated circuits, photonics, and optoelectronic devices. The machines achieve their precision by combining the use of highly repeatable nano-resolution actuators and motion systems, and on-tool precision calibration that is typically required for assembled systems since the sub-system machining precision is inherently insufficient.

M. Meissl

Papers

Step and flash imprint lithography: Template surface treatment and defect analysis

Step and flash imprint lithography: Defect analysis

Template fabrication schemes for step and flash imprint lithography

Step and Flash Imprint Lithography: A Technology Review

Precision Flexure Mechanisms in High Speed Nanopatterning Systems