Measurements of hydrogen gas stopping efficiency for tin ions from laser-produced plasma

We present the results of a joint experimental and theoretical study of plasma expansion arising from Nd:YAG laser ablation (laser wavelength λ = 1.064 μm) of tin microdroplets in the context of extreme ultraviolet lithography. Measurements of the ion energy distribution reveal a near-plateau in the distribution for kinetic energies in the range 0.03-1 keV and a peak near 2 keV followed by a sharp fall-off in the distribution for energies above 2 keV. Charge-state resolved measurements attribute this peak to the existence of peaks centered near 2 keV in the Sn 3+ -Sn 8+ ion energy distributions. To better understand the physical processes governing the shape of the ion energy distribution, we have modelled the laser-droplet interaction and subsequent plasma expansion using two-dimensional radiation hydrodynamic simulations. We find excellent agreement between the simulated ion energy distribution and the measurements both in terms of the shape of the distribution and the absolute number of detected ions. We attribute a peak in the distribution near 2 keV to a quasi-spherical expanding shell formed at early times in the expansion.

Section: Introductionmentioning

confidence: 99%

High-energy ions from Nd:YAG laser ablation of tin microdroplets: comparison between experiment and a single-fluid hydrodynamic model

Hemminga

Poirier

Basko

et al. 2021

“…It shifts the charge state balance away from Sn 2+ toward Sn + . As Sn + ions have a larger stopping cross section than Sn 2+ ions [16], the production of Sn + ions is beneficial to stopping Sn ions escaping from an LPP plasma in a high charge state.…”

Section: Discussionmentioning

confidence: 99%

“…From an EUV source perspective, the actual abundances of singly and doubly charged Sn ions and thus, whether Sn 2+ ions get converted by electron capture into Sn + , impacts the Sn ion mitigation because the penetration depth of the Sn ions into the H 2 buffer gas depends on the stopping cross sections. Recent stopping measurements [16] hint at appreciably larger stopping powers for Sn + than for Sn 2+ ions.…”

Section: Introductionmentioning

confidence: 99%

Evidence of production of keV Sn⁺ ions in the H₂ buffer gas surrounding an Sn-plasma EUV source

Rai

Bijlsma

Poirier

et al. 2023

Charge-state-resolved kinetic energy spectra of Sn ions ejected from a laser-produced plasma (LPP) of Sn have been measured at different densities of the H2 buffer gas surrounding a micro-droplet LPP. In the absence of H2, energetic keV Sn ions with charge states ranging from 4+ to 8+ are measured. For the H2 densities used in the experiments no appreciable stopping or energy loss of the ions is observed. However, electron capture by Sn ions from H2 results in a rapid shift towards lower charge states. At the highest H2 pressure of 6×10−4 mbar, only Sn2+ and Sn+ ions are measured. The occurrence of Sn+ ions is remarkable due to the endothermic nature of electron capture by Sn2+ ions from H2. To explain the production of keV Sn+ ions, it is proposed that their generation is due to electron capture by metastable Sn2+∗ ions. The gateway role of metastable Sn2+∗ is underpinned by model simulations using atomic collision cross sections to track the charge states of Sn ions while traversing the H2 buffer gas.

“…The pressure of the buffer gas determines its Sn-ion stopping power. Stopping power is a function of the kinetic energy of the Sn ion [160]. Understanding Sn-H 2 collisions on the fundamental level is key to set the optimal pressure.…”

Section: Plasma Expansion: Ion Kinetic Energy Distributionsmentioning

confidence: 99%

Physics of laser-driven tin plasma sources of EUV radiation for nanolithography

Versolato

2019

122

Laser-produced transient tin plasmas are the sources of extreme ultraviolet (EUV) light at 13.5 nm wavelength for next-generation nanolithography, enabling the continued miniaturization of the features on chips. Generating the required EUV light at sufficient power, reliability, and stability presents a formidable multi-faceted task, combining industrial innovations with attractive scientific questions. This topical review presents a contemporary overview of the status of the field, discussing the key processes that govern the dynamics in each step in the process of generating EUV light. Relevant physical processes span over a challenging six orders of magnitude in time scale, ranging from the (sub-)ps and ns time scales of laser-driven atomic plasma processes to the several μs required for the fluid dynamic tin target deformation that is set in motion by them.