Multi-Diagnostic Characterization of Laser-Produced Tin Plasmas for EUV Lithography

TL;DR

This paper provides a comprehensive multi-diagnostic analysis of laser-produced tin plasmas for EUV lithography, revealing detailed plasma properties and emission origins to improve EUV source development.

Contribution

It introduces an integrated experimental platform combining Thomson scattering, interferometry, and spectroscopy for detailed plasma characterization in EUV lithography.

Findings

Electron temperatures and densities decay with distance from the target.

Thomson scattering and interferometry measurements agree well.

Most EUV emission originates within 150 μm of the target under suboptimal conditions.

Abstract

We present a comprehensive characterization of laser-produced tin (Sn) plasmas relevant to extreme ultraviolet (EUV) lithography using a multi-diagnostic suite integrated into the new experimental platform, "SparkLight". Tin plasmas are generated by irradiating a continuously moving tin-coated wire with laser pulses (1064 nm, 10 ns, up to $5.7\times10^{10}$ W/cm$^2$) and probed via coherent Thomson scattering, laser interferometry, and EUV emission spectroscopy. Thomson scattering measurements reveal electron temperatures and densities that decay with distance from the target. Densities derived from Thomson scattering are cross-validated against laser interferometry, showing excellent agreement. Correlating the results of these laser diagnostics with spatially resolved EUV spectroscopy suggests that the bulk of useful EUV emission originates within 150 $\mu$m of the target and is generated under suboptimal plasma conditions. This work demonstrates a practical integrated approach for plasma characterization in EUV source development.