Laser-to-droplet alignment sensitivity relevant for laser-produced plasma sources of extreme ultraviolet light

TL;DR

This paper develops and experimentally validates a simple model that predicts how the tilt, expansion, and velocity of tin micro-droplets respond to laser alignment, crucial for EUV plasma sources in nanolithography.

Contribution

The paper introduces a minimal model with a single parameter to describe laser-to-droplet alignment sensitivity, aiding precise control in industrial EUV applications.

Findings

Model accurately predicts tilt angle sensitivity

Model validated through experiments with tin micro-droplets

Provides scaling laws for laser alignment control

Abstract

We present and experimentally validate a model describing the sensitivity of the tilt angle, expansion and propulsion velocity of a tin micro-droplet irradiated by a 1 {\mu}m Nd:YAG laser pulse to its relative alignment. This sensitivity is particularly relevant in industrial plasma sources of extreme ultraviolet light for nanolithographic applications. Our model has but a single parameter: the dimensionless ratio of the laser spot size to the effective size of the droplet, which is related to the position of the plasma critical density surface. Our model enables the development of straightforward scaling arguments in turn enabling precise control the alignment sensitivity.