Electromagnetic modeling of near-field phase-shifting contact lithography with broadband ultraviolet illumination

TL;DR

This paper models electromagnetic absorption in near-field phase-shifting contact lithography using broadband UV light, revealing how geometric parameters and illumination spectrum influence feature resolution and quality.

Contribution

It introduces a rigorous coupled-wave analysis for broadband UV illumination in contact lithography, highlighting the impact on feature resolution and profile.

Findings

Columnar features are higher quality with broadband illumination.

Feature resolution can be less than 100 nm with broadband UV in TM mode.

Groove depth in the mask significantly affects feature profile.

Abstract

Near-field phase-shifting contact lithography is modeled to characterize electromagnetic absorption in a photoresist layer with one face in contact with a quartz binary phase-shift mask. The broadband ultraviolet illumination is represented as a frequency-spectrum of normally incident plane waves. A rigorous coupled-wave analysis is carried out to determine the absorption spectrum of the photoresist layer. The specific absorption rate in the photoresist layer is calculated and examined in relation to the geometric parameters. Columnar features in the photoresist layer are of higher quality on broadband illumination in contrast to monochromatic illumination, in conformity with some recent experimental results. Feature resolution and profile are noticeably affected by the depth of the grooves in the phase-shift mask. Ideally, the feature linewidth can be less than about 100 nm for broadband illumination in the transverse-magnetic mode. These conclusions are subject to modification by the photochemistry-wavelength characteristics of the photoresist.