Accessible Unlicensed Requires Authentication Published by De Gruyter June 12, 2019

Fabrication of 3D microstructures using grayscale lithography

Frederico Lima, Isman Khazi ORCID logo, Ulrich Mescheder, Alok C. Tungal and Uma Muthiah

Abstract

Following the demand for three-dimensional (3D) micromachined structures, additive and subtractive processes were developed for fabrication of real 3D shapes in metals, alloys and monocrystalline Si (c-Si). As a primary structuring step for well-defined 3D structuring of the photoresist, grayscale lithography by laser direct writing was used. For additive fabrication of 3D microstructures, structured photoresist was used as molds. They were sputtered and subsequently electroplated by a metal (Cu) and an alloy (NiCo). The derived electroplated structures were demolded from the photoresist using an organic stripper. These metal structures are satisfactory replicas of the photoresist pattern. For subtractive pattern transfer of 3D structures into c-Si, reactive ion etching (RIE) was used to transfer the 3D photoresist structure into c-Si with 1:1 pattern transferability. The process parameters of RIE were optimized to obtain a selectivity of 1 and an anisotropy factor close to 1. Whereas conventional X-ray lithography (LIGA) and nanoimprint lithography result in 2.5D patterns, these techniques allow the fabrication of almost any arbitrary 3D shapes with high accuracy. In many cases, 3D structures (‘free forms’) are required, e.g. for molding of optical components such as spheres (or aspheres), channels for lab-on-a-chip and pillars for biological applications. Moreover, 3D structures on Si could be used as optical gratings and sensors.

Acknowledgments

We would like to thank Mr. Alexander Filbert for the technical support with the grayscale lithography using DWL 66FS and the DFG for the grant for the DWL 66FS (under INST 897/4-1 FUGG).

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Received: 2019-02-27
Accepted: 2019-04-01
Published Online: 2019-06-12
Published in Print: 2019-06-26

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