Cross-calibration of a combined electrostatic and time-of-flight analyzer for energy- and charge-state-resolved spectrometry of tin laser-produced plasma

Abstract

We present the results of the calibration of a channeltron-based electrostatic analyzer operating in time-of-flight mode (ESA-ToF) using tin ions resulting from laser-produced plasma, over a wide range of charge states and energies. Specifically, the channeltron electron multiplier detection efficiency and the spectrometer resolution are calibrated, and count rate effects are characterized. With the obtained overall response function, the ESA-ToF is shown to accurately reproduce charge-integrated measurements separately and simultaneously obtained from a Faraday cup (FC), up to a constant factor the finding of which enables absolute cross-calibration of the ESA-ToF using the FC as an absolute benchmark. Absolute charge-state-resolved ion energy distributions are obtained from ns-pulse Nd:YAG-laser-produced microdroplet tin plasmas in a setting relevant for state-of-the-art extreme ultraviolet nanolithography.

Energy- and charge-state-resolved spectrometry of tin laser-produced plasma using a retarding field energy analyzer

“…Assuming an alignment of the grids where the grids are spaced such that they have minimal geometric overlap but the same orientation, the total transmission may be estimated to be 41 %. This figure was previously found to be consistent with an ion current comparison between the RFA and a grid-less Faraday cup [11].…”

“…Ions with higher charge may still be present but at negligible quantities. The individual charge-energy spectra follow trends similar to those seen previously using an electrostatic time-of-flight analyzer [11,22], with in particular the higher charge states bunching up to form the aforementioned high-energy peak.…”

“…In a previous experiment [11], we confirmed the gain of the trans-impedance amplifier to be equal to its expected value of 25 kV/A. Measured ion transients have a typical duration on the order of several 10 μs .…”

“…A wide variety of ion diagnostic tools has been used in the literature, e.g., electrostatic probes [6]; charge-integrated Faraday cups (FC) [7,8]; charge-resolved retarding field analyzers (RFA) [9,10]; electrostatic analyzers (ESA) [11][12][13][14][15]; and Thompson parabolas (TPS) [16]. Recently, the ARCNL ESA was cross-calibrated with a 4-grid FC, in an effort to produce high-accuracy charge-resolved ion spectra [11].…”

Microdroplet-tin plasma sources of EUV radiation driven by solid-state-lasers (Topical Review)

“…The experimental measurements indicate a nearplateau in the ion energy distribution for kinetic energies in the 0.03-1 keV range, a peak near 2 keV followed by a sharp fall-off in the distribution for energies above 2 keV (red curve in figure 7). Charge-state resolved measurements, performed with a cross-calibrated electrostatic analyzer in time-of-flight mode (ESA-ToF) [107], attributed this peaked feature at 2 keV to the existence of peaks (centered near 2 keV) in the Sn 3+ − Sn 8+ ion energy distributions. To understand the physical origin of this peaked feature, Hemminga et al [106] performed two-dimensional simulations of the plasma initiation, growth and subsequent expansion using the radiation hydrodynamic code RALEF-2D.…”