Controlling ion kinetic energy distributions in laser produced plasma sources by means of a picosecond pulse pair

TL;DR

This paper introduces a novel picosecond pulse pair scheme for laser-produced plasma sources that reduces fast ion debris, improves target shaping, and enhances EUV lithography efficiency.

Contribution

It proposes a new pre-pulse method using a picosecond pulse pair to control ion energy distributions in plasma sources for EUV lithography.

Findings

Reduces fast ion debris in plasma sources.

Enables tailored target shaping.

Avoids back-reflections to lasers.

Abstract

The next generation of lithography machines uses extreme ultraviolet (EUV) light originating from laser-produced plasma (LPP) sources, where a small tin droplet is ionized by an intense laser pulse to emit the requested light at 13.5 nm. Numerous irradiation schemes have been explored to increase conversion efficiency (CE), out of which a double-pulse approach comprising a weak picosecond Nd:YAG pre-pulse followed by a powerful pulse is considered to be very promising [1]. Nevertheless, even for such CE-optimized schemes, ion debris ejected from the plasma with kinetic energies up to several keV remain a factor that hampers the maximum performance of LPP sources. In this letter we propose a novel pre-pulse scheme consisting of a picosecond pulse pair at 1064 nm, which decreases the amount of undesirable fast ions, avoids back-reflections to the lasers and enables one to tailor the target shape.