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Title:Detection of energetic neutral flux emanating from extreme ultraviolet light lithography sources
Author(s):Sporre, John R.
Advisor(s):Ruzic, David N.
Department / Program:Nuclear, Plasma, & Rad Engr
Discipline:Nuclear Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Extreme Ultraviolet (EUV)
debris mitigation
neutral debris
energetic neutrals
XTS 13-35
neutral detector
Ion Flux
Neutral Flux
source debris
Abstract:The advancement of the semiconductor industry depends on the improvement and advancement of the processes involved in creating integrated circuits. The most critical of these processes, lithography, is currently at a point where novel alternative techniques must be developed for further reduction in circuitry dimensions. One of the most promising techniques for the next generation of lithography is extreme ultraviolet light lithography (EUVL) technology. This technique improves upon currently used excimer laser lithography by reducing the light source wavelength from 195nm down to a 13.5nm ± 0.2 nm. This shift allows for an increase in resolution without the traditional consequences of a reduced depth of focus. Such a drastic reduction in wavelength is not without any technological hurdles. One such hurdle is the existence of energetic debris emitted by the dense warm plasmas (~1019cm-3, ~30 eV) used to create the EUV light. EUV’s high absorbance into most known materials prevents the traditional use of a pellicle to protect the collection optics, which reflect the produced light to an intermediate focus location. The debris limits the lifetime of the collector optics, and leads to a critical increase in cost of ownership. As such there is a necessity to incorporate new debris mitigation methods, as well as be able to quantify the effectiveness of these techniques. In this work, both a theoretical and experimental approach is taken to investigate the development of energetic neutral species. The development, and expansion principle, of energetic ions in an EUV plasma is explained with a self-similar hydrodynamic developed by Murakami. This model explains that rapidly accelerated electrons, emitted from destabilized EUV plasma, create an electric potential that accelerates ions to high energies. The higher charge state species, produced in part by ionization processes, are more rapidly accelerated by the electric potential, producing higher energy ions. Yet, a significant set of recombination processes allow for the neutralization of energetic low charge ion species. By neutralizing lowly ionized high-energy species, energetic neutral species are created. It is these species that are investigated in this body of work. A neutral detector was developed in order to quantitatively analyze the energetic neutral flux emanating from EUV sources. Utilizing this detector, and a Xe-fueled XTREME XTS 13-35 EUV source, the effects of debris mitigation is investigated. It will be shown that without debris mitigation, neutral flux accounts for approximately 78% of the total energetic flux emanating from the EUV source, with approximately 2x105 neutrals/cm2-pulse being observed. Incorporating maximum debris mitigation reduces this fraction to 54% while reducing the neutral flux by an order of magnitude. Debris mitigation also lowers the peak energy of the neutral spectrum by nearly 50% from 14 keV to 7 keV. Low energy neutral debris measurements of a modified Sn-fueled EUV source will also be presented, revealing that between 0 and 5 keV, neutrals account for approximately half of the total flux observed. Ultimately the development of this detector reveals the need for energetic neutral flux characterization, and the need to mitigate this debris.
Issue Date:2010-08-20
Rights Information:Copyright 2010 JOHN R. SPORRE
Date Available in IDEALS:2010-08-20
Date Deposited:2010-08

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