Phase mask pinholes as spatial filters for laser interference lithography

TL;DR

This paper demonstrates the fabrication and application of phase mask pinholes as spatial filters in laser interference lithography, significantly improving feature size uniformity across the substrate.

Contribution

It introduces a novel phase mask design for pinholes in LIL, enhancing beam uniformity and exposure consistency, which was not previously achieved.

Findings

Feature dimension variation reduced from 47.2% to 27.5%.

First successful fabrication of phase mask pinholes.

Improved uniformity in laser interference lithography.

Abstract

Laser resonators have outputs with Gaussian spatial beam profiles. In laser interference lithography (LIL), using such Gaussian shaped beams leads to an inhomogeneous exposure of the substrate. As a result, dimensions of lithography defined features vary significantly across the substrate. In most LIL setups, pinholes are used as filters to remove optical noise. Following a concept proposed by Hariharan et. al. a phase mask can be added to these pinholes. In theory, this modification results in a more uniform beam profile, and, if applied as spatial filters in LIL, in improved exposure and hence feature size uniformity. Here, we report on the first successful fabrication of such elements and demonstrate their use in an LIL setup to reduce feature dimension variations from 47.2% to 27.5% using standard and modified pinholes, respectively.