Abstract
We experimentally study the morphology of a radially expanding sheet of liquid tin, formed by nanosecond-pulse Nd:YAG laser impact on a spherical microdroplet. Specifically, the sheet thickness profile and its time evolution are captured in detail over a range of laser-pulse energies and for two droplet sizes. Two complementary methods to determine this thickness are employed and shown to be in excellent agreement. All obtained thickness profiles collapse onto a single self-similar curve. Spatial integration of the thickness profiles allows us to determine the volume of the sheet. Remarkably, less than half of the initial amount of tin remains in the sheet under conditions relevant for industrial sources of extreme ultraviolet light, where these thin tin sheets serve as target material. Further analysis shows that the dominant fraction of the mass lost from the sheet during its expansion ends up as fine fragments. We propose that such mass loss can be minimized by producing the sheet targets on the shortest possible time scale. These findings may be particularly valuable for ongoing developments in state-of-the-art nanolithography.
Highlights
Tin microdroplets serve as mass-limited targets for highenergy lasers to produce a hot and dense plasma that emits extreme ultraviolet (EUV) light for state-of-the-art nanolithography [1,2,3,4,5,6,7]
Less than half of the initial amount of tin remains in the sheet under conditions relevant for industrial sources of extreme ultraviolet light, where these thin tin sheets serve as target material
We experimentally study the morphology of a radially expanding sheet of liquid tin formed upon nanosecondpulse laser impact on a spherical microdroplet under conditions relevant for EUV lithography
Summary
Tin microdroplets serve as mass-limited targets for highenergy lasers to produce a hot and dense plasma that emits extreme ultraviolet (EUV) light for state-of-the-art nanolithography [1,2,3,4,5,6,7]. The generation of EUV light is a two-step process, in which a first laser prepulse deforms the tin droplet into a liquid sheet that is suited to serving as a target for a second, more energetic main laser pulse that produces the EUV light. Several recent studies have provided insight into the response of a tin microdroplet to a nanosecond laser pulse in which the propulsion [10,11] accompanies a deformation [10,11,12,13,14] of the droplet into a thin sheet.
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