Nanoimprint lithography (NIL) is a high throughput, high-resolution parallel patterning method in which a surface pattern of a stamp is replicated into a material by mechanical contact and three dimensional material displacement. This can be done by shaping a liquid followed by a curing process for hardening, by variation of the thermomechanical properties of a film by heating and cooling, or by any other kind of shaping process using the difference in hardness of a mold and a moldable material. The local thickness contrast of the resulting thin molded film can be used as a means to pattern an underlying substrate on wafer level by standard pattern transfer methods, but also directly in applications where a bulk modified functional layer is needed. Therefore it is mainly aimed toward fields in which electron beam and high-end photolithography are costly and do not provide sufficient resolution at reasonable throughput. The aim of this review is to play between two poles: the need to establish standard processes and tools for research and industry, and the issues that make NIL a scientific endeavor. It is not the author’s intention to duplicate the content of the reviews already published, but to look on the NIL process as a whole. The author will also address some issues, which are not covered by the other reviews, e.g., the origin of NIL and the misconceptions, which sometimes dominate the debate about problems of NIL, and guide the reader to issues, which are often forgotten or overlooked.

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Nanoimprint lithography: An old story in modern times? A review

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

A continuous roll-to-roll nanoimprint lithography (R2RNIL) technique can provide a solution for high-speed large-area nanoscale patterning with greatly improved throughput; furthermore, it can overcome the challenges faced by conventional NIL in maintaining pressure uniformity and successful demolding in large-area imprinting. In this work, we demonstrate large-area (4 in. wide) continuous imprinting of nanogratings by using a newly developed apparatus capable of roll-to-roll imprinting (R2RNIL) on flexible web and roll-to-plate imprinting (R2PNIL) on rigid substrate. The 300 nm line width grating patterns are continuously transferred on either glass substrate (roll-to-plate mode) or flexible plastic substrate (roll-to-roll mode) with greatly enhanced throughput. In addition, the film thickness after the imprinting process, which is critical in optical applications, as a function of several imprinting parameters such as roller pressure and speed, is thoroughly investigated, and an analytical model has been developed to predict the residual layer thickness in dynamic R2RNIL process.

Large-area roll-to-roll and roll-to-plate nanoimprint lithography: a step toward high-throughput application of continuous nanoimprinting.

The effects of polymeric nanostructure shape on drug delivery.

Elastomeric stamps facilitate direct patterning of electrical, biological, chemical, and mechanical materials A thin film of material is deposited on a substrate The deposited material, either originally present as a liquid or subsequently liquefied, is patterned by embossing at low pressure using an elastomeric stamp having a raised pattern The patterned liquid is then cured to form a functional layer The deposition, embossing, and curing steps may be repeated numerous times with the same or different liquids, and in two or three dimensions The various deposited layers may, for example, have varying electrical characteristics, interacting so as to produce an integrated electronic component

Fabrication of finely featured devices by liquid embossing

An alternative approach to lithography is being developed based on a dual-layer imprint scheme. This process has the potential to become a high-throughput means of producing high aspect ratio, high-resolution patterns without projection optics. In this process, a template is created on a standard mask blank by using the patterned chromium as an etch mask to produce high-resolution relief images in the quartz. The etched template and a substrate that has been coated with an organic planarization layer are brought into close proximity. A low-viscosity, photopolymerizable formulation containing organosilicon precursors is introduced into the gap between the two surfaces. The template is then brought into contact with the substrate. The solution that is trapped in the relief structures of the template is photopolymerized by exposure through the backside of the quartz template. The template is separated from the substrate, leaving a UV-curved replica of the relief structure on the planarization layer. Features smaller than 60 nm in size have been reliably produced using this imprinting process. The resolution silicon polymer images are transferred through the planarization layer by anisotropic oxygen reactive ion etching. This paper provides a progress report on our efforts to evaluate the potential of this process.

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M. Wedlake

Papers

Step and flash imprint lithography: a new approach to high-resolution patterning