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Title:Reduced density hydrogenated silicon through reactive dc magnetron sputtering with secondary rf plasma discharge for EUV multilayer mirror application
Author(s):Uhlig, Jan Peter
Advisor(s):Ruzic, David N
Contributor(s):Andruczyk, Daniel
Department / Program:Nuclear, Plasma, & Rad Engr
Discipline:Nuclear, Plasma, Radiolgc Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Reduced Density Si
Multilayer Mirror
Abstract:In Extreme Ultra-violet Lithography applications Si/Mo Multi-Layer Mirrors are used to collect, transmit and focus EUV light. While current MLMs have reached the practical limit achievable with current materials, the per mirror efficiency is still suboptimal, especially in a projection lithography system with a multitude of these mirrors. A method of improvement then, without significantly modifying the mirror itself or the process for manufacture of the mirrors, is to replace the Si spacer layer found in EUV mirrors, with a reduced density Si layer. Theory predicts that such a modification, if done without introducing contaminants that absorb EUV themselves, can marginally increase the per mirror efficiency. When this per mirror marginal improvement is then applied to all mirrors in a lithography system the end result comes out to be a two-fold or more increase in efficiency of the system. Investigated in this work then is a method for replacing the Si film with a reduced density Si:H film, through the modification of the standard DCMS deposition process through reactive DCMS with hydrogen, along with a secondary RF plasma to aide in radical generation. The eventual goal is to produce both hydrogenated and non-hydrogenated MLMs to the same specifications, which can then be tested for EUV reflectivity, proving the initial theory. In the process for producing the low density hydrogenated Si film discussed the main issue that presented itself was the formation of H2 gas blisters in the film, likely at subsurface interfaces, leading to structures that project beyond the surface of the film. Methods for the avoidance of these blisters are discussed and applied, leading, among others, to Si:H films with a density of 1.73 g/cm3, with lesser numbers and smaller blisters than previously observed. Finally, successful attempts are also made at producing multilayers at the appropriate size for EUV reflectivity, that is with a bilayer thickness of 6.9 nm.
Issue Date:2019-07-18
Rights Information:Copyright 2019 Jan Uhlig
Date Available in IDEALS:2019-11-26
Date Deposited:2019-08

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