Making large overhangs in micrometer and nanometer-sized structures

TL;DR

This paper presents two innovative fabrication procedures for creating microstructures with large overhangs and high aspect ratios, combining angled dry etching and wet etching, with a derived formula for process optimization.

Contribution

It introduces two general methods for fabricating large overhangs in microstructures, including a novel time-dependent etch process with a formula to control attack angles.

Findings

The first method effectively creates overhangs using static angled dry etching.

The second method reduces lithography steps with a time-dependent etch process.

A formula is derived to predict the attack angle evolution during etching.

Abstract

We describe two general procedures for fabricating microstructures with large overhangs and high aspect-ratio support pillars. The first method uses a static angled dry etch on micro- or nano-pillars to create an initial overhang, followed by wet etching for further erosion. The second method uses a time-dependent angled etch on a flat plane patterned with protective resin, to reduce the number of lithography steps needed to make these objects. The time-dependent dry etch is again followed by a wet etch. For the second method we derive a formula that provides the rate at which the attack angle must evolve, given a known etch rate within the target material, the depth of the desired overhang (undercut), and the instantaneous attack angle.