Stable droplet generator for a high brightness laser produced plasma extreme ultraviolet source

Abstract

We present the results of the low-melting liquid metal droplets generation based on excited Rayleigh jet breakup. We discuss on the operation of the industrial and in-house designed and manufactured dispensing devices for the droplets generation. Droplet diameter can be varied in the range of 30-90 μm. The working frequency of the droplets, velocity, and the operating temperature were in the ranges of 20-150 kHz, 4-15 m/s, and up to 250 °C, respectively. The standard deviations for the droplet center of mass position both their diameter σ < 1 μm at the distance of 45 mm from the nozzle. Stable operation in the long-term (over 1.5 h) was demonstrated for a wide range of the droplet parameters: diameters, frequencies, and velocities. Physical factors affecting the stability of the generator operation have been identified. The technique for droplet synchronization, allowing using the droplet as a target for laser produced plasma, has been created; in particular, the generator has been successfully used in a high brightness extreme ultraviolet (EUV) light source. The operation with frequency up to 8 kHz was demonstrated as a result of the experimental simulation, which can provide an average brightness of the EUV source up to ∼1.2 kW/mm sr.

Shaping and Controlled Fragmentation of Liquid Metal Droplets through Cavitation

“…Liquid metal droplets of Sn-In eutectic (48–52% mass stoichiometry) alloy were generated with an in-house-made droplet generator utilizing stimulated jet breakup. Technical specification of the droplet generator can be found in our previous publication 45 . The temperature of the alloy in the system was maintained at 140 °C, which is 20 °C higher than the melting temperature of the Sn-In eutectic.…”

The precise and accurate production of millimetric water droplets using a superhydrophobic generating apparatus

“…Hanging pendant [22][23][24][25][26] Narrow range in the spread of droplet diameters Generation of one droplet size per dispensing tip/liquid combination Forced pendant 12,13 Narrow range in the spread of droplet diameters Considerable droplet oscillations during descent due to burst gas-induced perturbations Production of droplets with masses less than the Droplets tend to not follow a prescribed trajectory. critical mass for gravitational detachment Pneumatic pressure wave 15,20 Production of droplets with diameters Generation of one droplet size per dispensing smaller than the pendant methods tip/liquid combination High ease of use Production of abnormally large or small droplets not uncommon Cohesive breakup of the liquid jet results in stochastic production of satellite droplets and high degree of oscillation Droplets tend to not follow a prescribed trajectory Piezoelectric pressure wave 14,16,18,20 Production of droplets with diameters down Requires optimization of frequency/amplitude of to the diameter of the dispensing tip piezoelectric element flexion for each small range of droplet diameters and liquid desired High ease of use and high speed of droplet Cohesive breakup of the liquid jet results in generation stochastic production of satellite droplets and high degree of oscillation Droplets tend to not follow a prescribed trajectory Rayleigh stream breakup 19,30,31 Production of droplets with high diameter Produces a stream of droplets; no single droplet precision production capability High speed of droplet generation preventing droplet ejection. High Re liquids, however, result in the production of a large number of satellite droplets, 18,19 We = ν min ρd nozzle σ > 4, (3)…”

“…Many applications, however, necessitate a single droplet whose production can be accurately timed. 19,30,31 The positive and negative attributes of the currently employed droplet generation techniques are summarized in Table I. The problems inherent to the existing methods of droplet generation can be attributed to two factors: (1) separating a desired volume of liquid from the bulk supply and (2) detachment of the liquid from the solid generating tip.…”

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

“…On one extreme end, short fsps laser pulses create bubble-like targets (see figure 1 bottom panel) as described by, e.g. Kurilovich et al [15] (also see [16][17][18][19][20]) and more recently by De Faria Pinto et al [21] addressing also laser polarization dependencies. On the other extreme end, long (ns) laser pulses create strongly propelled, flattened targets (see figure 1 upper panel).…”