Protecting EUV mirrors: how tin and plasma shape hydrogen uptake in ruthenium films
Shih-Chi Wang defended his PhD thesis at the Department of Applied Physics and Science Education on October 9.
Shih-Chi Wang has investigated how hydrogen interacts with ruthenium films under plasma exposure, an issue critical to the performance and longevity of mirrors used in Extreme Ultraviolet Lithography (EUVL). His findings offer new insights into how tin contamination accelerates hydrogen uptake, potentially leading to blistering and degradation of these essential components in semiconductor manufacturing.
EUV mirrors under pressure
EUVL is a key technology for producing advanced semiconductor chips. In EUVL machines, EUV light is guided through a series of mirrors, typically capped with ruthenium films, to create nanoscale patterns on silicon wafers. These mirrors are exposed to tin debris and hydrogen plasmas, which can cause hydrogen uptake and retention in the ruthenium layer. Over time, this can lead to blister formation and mirror failure.
Wang鈥檚 research focused on understanding the factors that influence this uptake, particularly the role of tin. His experiments revealed that native oxide layers on ruthenium delay hydrogen absorption, while even a single atomic layer of tin dramatically accelerates it, by nearly three orders of magnitude.
Plasma experiments and modeling
To study this process, Wang used hydrogen plasma and measured uptake rates in ruthenium-capped systems, leveraging tools and techniques from nuclear fusion research. He introduced a novel dual-sensor radical probe to measure ion and atomic fluxes, and used a titanium absorption layer to quantify hydrogen retention.
He also applied a reaction-diffusion model, adapted from fusion research, to simulate the behavior of hydrogen in the ruthenium-tin system. The model helped explain the observed delay and acceleration effects, providing a deeper understanding of the underlying mechanisms.
His work not only clarifies how tin influences plasma-induced hydrogen uptake, but also offers practical solutions to protect EUV mirrors, supporting the continued advancement of next-generation semiconductor technologies.
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Supervisors
Thomas Morgan and Shuxia Tao