Effect of focal spot size on in-band 135 nm extreme ultraviolet emission from laser-produced Sn plasma

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Laser-produced plasmas (LPP) from Sn targets are seriously considered to be the light source for extreme ultraviolet (EUV) next generation lithography, and optimization of such a source will lead to improved efficiency and reduced cost of ownership of the entire lithography system. We investigated the role of reheating a prepulsed plasma and its effect on EUV conversion efficiency (CE). A 6 ns, 1.06 lm Nd:yttrium aluminum garnet laser was used to generate the initial plasma that was then reheated by a 40 ns, 10.6 lm CO 2 laser to generate enhanced EUV emission from a planar Sn target. The effects of prepulsed laser intensity and delay timings between the prepulsed and the pumping pulse were investigated to find the optimal pre-plasma conditions before the pumping pulse. The initial optimization of these parameters resulted in 25% increase in CE from the tin LPP. The cause of increased EUV emission was identified from EUV emission spectra and ion signal data.

Section: Resultsmentioning

confidence: 99%

Enhancements of extreme ultraviolet emission using prepulsed Sn laser-produced plasmas for advanced lithography applications

Freeman

Harilal

Hassanein

2011

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“…However, at the same time, higher lateral expansion can be expected with smaller spot sizes. 2, 19 With a larger spot size, more EUV light can be generated due to high hydrodynamic coupling efficiency, but a longer plasma scale length results in heavier reabsorption and, hence, less EUV light can escape from the plasma. Hence, the final output of 13.5 nm EUV light with varying laser spot size is determined by the balance of the laser energy loss due to the lateral expansion and the reabsorption of EUV light which leads to constant CE irrespective of the laser spot size used.…”

Section: Resultsmentioning

confidence: 99%

“…16 We recently reported that the spot size has negligible effect on the conversion efficiency ͑CE͒ of in-band radiation ͑13.5 nm with 2% bandwidth͒. 19 The constant CE irrespective of the spot size is attributed to the balance of the laser energy loss due to lateral expansion of the plasma and reabsorption of the EUV light.…”

Section: Introductionmentioning

confidence: 99%

Influence of spot size on propagation dynamics of laser-produced tin plasma

Harilal¹

2007

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The plume dynamics in the presence of an ambient gas is very intriguing physics. The expansion of a laser-produced plasma in the presence of an ambient gas leads to internal plume structures, plume splitting, sharpening, confinement, etc. We investigated propagation dynamics of an expanding tin plume for various spot sizes using a fast visible plume imaging and Faraday cup diagnostic tools. Our results indicate that the sharpening of the plume depends strongly on the spot size. With a smaller spot size, the lateral expansion is found to be higher and the plume expansion is spherical while with a larger spot size the plume expansion is more cylindrical. Analysis of time resolved imaging also showed internal structures inside the plume.

“…The picosecond laser is used as a prepulse. The nanosecond laser is used to generate the EUV plasma to match the optimized conditions for efficient generation of 13.5 nm EUV light, 10 called as the pumping pulse hereafter. The two lasers are synchronized with a pulse delay generator ͑Stanford DG535͒ with a jitter less than 0.5 ns.…”

Section: Experimental Arrangementsmentioning

confidence: 99%

Investigation of the interaction of a laser pulse with a preformed Gaussian Sn plume for an extreme ultraviolet lithography source

Tao

Tillack

Harilal

et al. 2007

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The interaction of a laser pulse with a Sn preplasma formed by a low energy prepulse was investigated for an extreme ultraviolet ͑EUV͒ lithography light source. A much lower ion kinetic energy and nearly the same conversion efficiency from laser to in-band ͑2% bandwidth͒ 13.5 nm EUV light were simultaneously observed as compared with those from the direct interaction with a solid surface. The reason comes from the interaction of the laser pulse with a smooth preplume induced by the prepulse. The density profile of the preplume was measured with time-resolved shadowgraphy and could be fitted with a Gaussian function. The energy of the ions located at the flux peak E p scales with the length of the preplume l s as E p ϰ 1/l s . Laser absorption in the low-density preplume and ion acceleration during plasma expansion are discussed. This result provides a general way to control particle energy from a laser plasma interaction.