Replication of 3D patterns from a grayscale resist master by nanoimprint process

Abstract

First, Grayscale I-Line lithography process developed in CEA-Leti allows to manufacture a variety of 3D patterns based on the well-known photolithography technology. Grayscale photolithography is an innovative and alternative approach to create 3D patterns such as microlenses for example. Exposure of a low contrast resist at different doses results in different thicknesses in the resist film. The variation of the intrinsic dose is obtained by using a binary mask that has different chromium densities, thus modulating the exposure intensity on the resist surface1. Secondly, the NanoImprint Lithography (NIL) is a technology capable of reproducing a wide morphological range. NIL is increasingly requested for the reproduction of 3D patterns. Initially, standard NIL process uses a hard master usually composed of Si or SiO2. The proposed work validates the quality of the replication by the NanoImprint process of a "resist master" created by grayscale lithography. This approach facilitates the manufacturing process of a master by avoiding the etching step and offering a cost-effective solution. The measurement of several types of 3D patterns are performed before and after replication during this study. CD preservation is evaluated for 32 types of microlenses simultaneously replicated. Finally, the combination of the Grayscale and NanoImprint technologies allows to considerably increasing the printing possibilities. By freeing the difficulties of multiple patterns morphology conservation during the etching, the replication of a resist master permits other potential applications, particularly in the optical field.