Patterning of Polymer Arrays with Enhanced Aspect-Ratio Using Hybrid Substrate Conformal Imprint Lithography

Abstract

Ultraviolet Substrate Conformal Imprint Lithography (SCIL) is an economic nanolithography technique of imprinting high-fidelity patterns over large areas. It is an improvement to conventional UV-Nanoimprint lithography (NIL) with high resolution, flexibility and conformal imprinting. However the aspect-ratio of SCIL is limited due to its patterning by capillary forces and the PDMS material has very low Young’s modulus (<2Mpa) hence, resulting in deformation of the feature sizes during the imprint process. In general the residual layer between the imprinted structures is etched away to obtain high aspect ratio. But in industrial applications an array of different 3D patterns are imprinted in a single step, thus, the residual layer of each structure depends on its volume and viscosity of the imprint material, thereby making the etching process impossible to increase the feature size and aspect-ratio of each microstructure individually. Hence in this paper a new SCIL stamp technique is demonstrated to implement an enhancement of aspect ratio. In this process, a flexible polymer material, Polydimethylsiloxane (PDMS) is used as the stamp material. The heights of the structure on the stamp are supported by a metal layer (higher Young’s modulus), which provides higher stiffness and rigidity to the stamp and thereby avoiding distortion of the patterns on the stamp. Also the metal layer acts as an UV blocking mask: hence while patterning on an UV curable imprint material, the residual edges of the microstructures, which are subjected to decrease the feature size, are removed in the development process of the uncured polymer areas. Thus, irrespective of the number and shape of the microstructures, an enhancement of aspect ratio is attained in a single step. Conventional imprinting of circular polymer arrays with dimensions 90μm / 70nm on their master template resulted in increased feature size up to 150 μm, while the height varied between 90-66nm and thereby decreasing the aspect ratio. Imprinting with the proposed SCIL technique resulted in 96 μm / 74nm dimension, thus around 60 μm of feature size improvement is achieved