Nanoimprint lithography: 2D or not 2D? A review

Abstract

Nanoimprint lithography (NIL) is more than a planar high-end technology for the patterning of wafer-like substrates. It is essentially a 3D process, because it replicates various stamp topographies by 3D displacement of material and takes advantage of the bending of stamps while the mold cavities are filled. But at the same time, it keeps all assets of a 2D technique being able to pattern thin masking layers like in photon-and electron-based traditional lithography. This review reports about 20 years of development of replication techniques at Paul Scherrer Institut, with a focus on 3D aspects of molding, which enable NIL to stay 2D, but at the same time enable 3D applications which are ''more than Moore.'' As an example, the manufacturing of a demonstrator for backlighting applications based on thermally activated selective topography equilibration will be presented. This technique allows generating almost arbitrary sloped, convex and concave profiles in the same polymer film with dimensions in micro-and nanometer scale.

High-aspect-ratio nanoimprint process chains

“…They are therefore characterized by an intermediate state between two-and threedimensional (2D and 3D), that is, a 2D planar design that is extended into the vertical dimension and often called 2½-D (Ref. 11). There are several methods to produce HAR structures on typical planar substrates, most of them relying on the anisotropy of subtractive pattern transfer of a low AR masking layer into an underlying resist or substrate, that is, by using mask based ultraviolet (UV)-photolithography (PL) with an AR up to 5, silicon etching (for example, dry etching) with an AR up to 20, and direct write laser lithography (DWL) and X-ray lithography with ARs 420 (Refs.…”

Complex 3D structures via hybrid processing of SU-8

“…The preparation of stamps for nanoimprint in SU-8 was demonstrated by combining thermal and UV nanoimprint [9] and by combining thermal nanoimprint with conventional photolithography [10]. Some of the techniques applied to prepare 3D structures have recently been reviewed [11]. Generally, whenever writing techniques like EBL or FIB are involved, the preparation is time-consuming and costly on case that large areas are envisaged.…”

Nanostructures induced light harvesting enhancement in organic photovoltaics

“…Imprint processing is a fabricating technology for embossed structures based on the physical modeling method and transfers the embossed templates to the surface of samples [49,50]. NIL with high resolution, excellent yield and low cost was first developed by S. Chou from the University of Minnesota in 1995 [51].…”