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Title:Hydrogen surface wave plasma cleaning of the EUV collector
Author(s):Panici, Gianluca
Director of Research:Ruzic, David N
Doctoral Committee Chair(s):Ruzic, David N
Doctoral Committee Member(s):Curreli, Davide; Jurczyk, Brian; Jin, Jianming
Department / Program:Nuclear, Plasma, & Rad Engr
Discipline:Nuclear, Plasma, Radiolgc Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):surface wave plasma
Abstract:Moore’s law states that the number of transistors on an integrated circuit doubles every two years. To maintain this pace, industry continues to innovate at each step of the manufacturing process. Novel methods are being investigated for the limiting step, lithography, to cut costs and drive innovation. The current industry standard of 193 nm light from an excimer laser has been manipulated through techniques such as multiple pattern or immersion lithography to reduce the wavelength and size of the features on the transistor. Going forward, a new technique, extreme ultraviolet (EUV) lithography, is being developed to replace existing technology. EUV light is generated by a laser-produced plasma as opposed to an excimer laser, bringing new challenges that must be overcome for the technology to be viable. One such challenge is the build-up of debris in the EUV source on the main optic (called the collector), reducing reflectivity and thus lowering power during operation. The tool must then be taken down to clean the collector outside of the vessel, introducing downtime and loss of profits. This work investigates a surface wave plasma-based in-situ cleaning method to restore reflectivity during EUV source operation. If the optic can continuously be cleaned, there is no need for tool downtime and profits increase. Previous plasma cleaning work has shown that the etch rate scales with the ion energy flux to the surface. Surface wave plasmas can take advantage of this by creating ions and radicals at the surface to be etched. Various surface wave antenna configurations have been characterized to determine viability for collector-scale etching. It was found that bright plasma was needed along the surface to reach etch rates greater than 10 nm/min. A model of the surface wave plasma was developed to understand hydrogen ion-Sn interactions and a validation experiment was conducted. In addition, a reactive ion sticking coefficient was empirically fit to the validation experiment data and used to predict etch rates. The experiment and simulation are compared with discrepancies identified and explained. Finally, simulations were carried to determine whether multiple antenna can be used to increase the plasma radius. The power scaling for each antenna was also simulated with the final result being the predicted power requirements for a two antenna system to etch the entire collector surface: an inner antenna of 4.1 kW and outer antenna of 9.8 kW is needed for the entire collector to have at least 10 nm/min etch rate.
Issue Date:2021-04-21
Rights Information:Copyright 2021 Gianluca Panici
Date Available in IDEALS:2021-09-17
Date Deposited:2021-05

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