Xenon Z-Pinch Discharge Plasma EUV Source Driven by Ultrashort Current Pulse

Abstract

The extreme ultraviolet (EUV) spectrum has significant interest both for basic science and for industrial applications, especially lithography-related studies. Discharge-produced plasma (DPP) EUV source efficiently generates EUV radiation. Current pulse parameter is the most important and sensitive factor in DPP EUV source, which is determined by the discharge loop inductance. This paper reports on shortening the current pulsewidth by reducing discharge loop inductance on a xenon gas Z-pinch DPP EUV source. The inherent inductance of the discharge loop was reduced to about 17 nH from the previous 34 nH, and the short-circuit current pulsewidth was shortened to 85 ns. Pulsewidth of discharge plasma current was only about 110 ns. DPP EUV source was characterized in terms of EUV signals (7–16 nm) and images. The experimental results show that a shorter current pulse produces sharper EUV signals. Ultrashort current pulse discharge radiated a sharp EUV signal with a narrow pulsewidth [full-width at half-maximum (FWHM)] of only 10 ns. Axial and radial sizes (FWHM) of EUV-emitting plasma were 2 mm and $400~\mu \text{m}$ , respectively. EUV source resembles an ellipse differing from the jet shape driven by longer current pulses. Thus, a DPP EUV source driven by an ultrashort current pulse may suit high temporal and spatial resolutions required for EUV application. Corresponding plasma dynamics are observed and discussed. A comparison of time-resolved visible and EUV light images indicates that EUV emission radiates from two adjacent stagnated hot plasma columns and localizes along the central axis. This also differs from longer current driven plasma dynamics, in which EUV emission radiates from the neck part between two separate cooler plasma zones and moves with the current flow. This implies that ultrashort current pulse may inhibit axial development of EUV-emitting plasma, thus improving EUV source spatial stability and reducing EUV radiation size.