Influence of spot size on extreme ultraviolet efficiency of laser-produced Sn plasmas

Abstract

We have investigated the spot size effects on the extreme ultraviolet conversion efficiency ͑CE͒ of CO 2 laser-produced Sn plasmas. The estimated CE of the laser to 13.5 nm radiation, within a 2% bandwidth, using a 10.6 m CO 2 laser with various pulse widths ͑25-55 ns͒ showed a double hump structure during a target-lens scan, where the CE is nearly 25% lower at the best focal position. Density analysis of the CO 2 laser-produced plasma showed steep density gradients at the best focal position, and a reduction in CE at the best focal position, which is explained by the lack of efficient coupling between the laser and the plasma.

Optimizing conversion efficiency and reducing ion energy in a laser-produced Gd plasma

“…By studying the effects of laser intensity on CE, the optimum laser intensity for irradiation of a given focal spot size can be defined. In general the flux required to maximize the CE 4 increases as the target radius decreases because of lateral expansion [16,17]. In the present work the laser intensity was varied from 10 11 −10 15 W/cm 2 to produce emission from Gd 12+ to Gd 25+ , whose resonant emission is around 6.7 nm [2,5,[18][19][20].…”

Influence of distance between sample surface and focal point on spectral intensity of nanosecond laser-induced silicon plasma in air

“…It could be attributed to many factors affecting the intensity, for example plasma overheating, opacity effects, energy losses due to plasma lateral expansion, differences in laser-plasma coupling cone angle, etc. 23 Carefully, as it can be seen in Fig. 4, the intensity of ionic line (N (II)) is higher than that of neutral line (Si (I)) when the surface of ablated sample is near the focal point.…”

Excitation wavelength dependence of water-window line emissions from boron-nitride laser-produced plasmas

“…One parameter that determines the density gradient in LPP is the spot size, where decreasing spot size increases the density gradient. 9 Both laser wavelength and spot size were varied in this experiment and contribute to the trends in line emission intensity.…”

“…Several possible sources that have been investigated for laboratory WW-microscopy are laser produced plasma (LPP), discharge produced plasma, 6 and electron excitation of oxygen. 7 Currently LPP have been extensively studied as sources for extreme ultraviolet lithography (EUVL) [8][9][10][11][12][13] due to their compact size, high brightness, and high conversion efficiency. The properties of EUV and SXR emission from LPP depend on target material and configuration, and on laser wavelength, temporal pulse width, and spot size.…”

“…[12][13][14] An EUV emission study using CO 2 laser (10.6 lm) and tin target showed that higher conversion efficiencies were attained for larger defocused spot sizes than for smaller minimal focal spot sizes. 9 In order to achieve efficient emission in the WW region LPP must be heated to much higher temperatures than is required for 13.5 nm EUVL source. Laser wavelength is one of the parameters that greatly affect LPP emission intensity in the WW region, as well as the opacity of the plasma.…”