Lithography tools are being built and shipped to semiconductor manufacturers for high volume manufacturing using extreme ultraviolet lithography (EUVL) at a wavelength of 13.5 nm. This wavelength is based on the availability of Mo/Si multilayer mirrors (MLMs) with a reflectivity of ∼70% at this wavelength. Moreover, the primary lithography tool manufacturer, ASML, has identified 6.x nm, where x∼7, as the wavelength of choice for so-called Beyond EUVL, based on the availability of La/B 4 C MLMs, with theoretical reflectance approaching 80% at this wavelength. The optimum sources have been identified as laser produced plasmas of Gd and Tb, as n = 4-n = 4 transitions in their ions emit strongly near this wavelength. However, to date, the highest conversion efficiency obtained, for laser to EUV energy emitted within the 0.6% wavelength bandwidth of the mirror is only 0.8%, pointing to the need to identify other potential sources or consider the selection of other wavelengths. At the same time, sources for other applications are being developed. Conventional sources for soft x-ray microscopy use H-like line emission from liquid nitrogen or carbon containing liquid jets which can be focused using zone plates. Recently the possibility of using MLMs with n = 4−n = 4 emission from a highly charged Bi plasma was proposed and subsequently the possibility of using Δn = 1 transitions in 3rd row transition elements was identified. All of these studies seek to identify spectral features that coincide with the reflectance characteristics of available MLMs, determine the conditions under which they are optimized and establish the maximum conversion efficiencies obtainable. Thus, there is a need for systematic studies of laser produced plasmas of a wide range of elements as some of the challenges are similar for all of these sources and some recent results will be presented.
We demonstrate efficient enhancement of soft X-ray (SXR) emission from molybdenum plasmas produced using dual pulse irradiation, in which 10-ns and 150-ps pre-pulses were followed by a 150-ps main pulse. The number of photons was observed to be 5.3 × 1016 photons/sr, which corresponded to a conversion efficiency of 1.5%/sr in λ = 2.34–4.38 nm region at a pulse separation time of 1 ns with the 150-ps pre-pulse. The conversion efficiency became 1.3 times as large as that produced by a single pulse. The results indicate the advantage of dual pulse irradiation using sub-ns pre-and main pulses to produce the bright plasmas required for applications such as laboratory based SXR microscopy.
The use of laser produced plasmas (LPPs) in extreme ultraviolet/soft x-ray lithography and metrology at 13.5 nm has been widely reported and recent research efforts have focused on developing next generation sources for lithography, surface morphology, patterning and microscopy at shorter wavelengths. In this paper, the spectra emitted from LPPs of the 2nd transition row elements from yttrium (Z = 39) to palladium (Z = 46), with the exception of zirconium (Z = 40) and technetium (Z = 43), produced by two Nd:YAG lasers which delivered up to 600 mJ in 7 ns and 230 mJ in 170 ps, respectively, are reported. Intense emission was observed in the 2–8 nm spectral region resulting from unresolved transition arrays (UTAs) due to 3d–4p, 3d–4f and 3p–3d transitions. These transitions in a number of ion stages of yttrium, niobium, ruthenium and rhodium were identified by comparison with results from Cowan code calculations and previous studies. The theoretical data were parameterized using the UTA formalism and the mean wavelength and widths were calculated and compared with experimental results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.