The photo-mechanism of EUV exposures in chemically amplified photoresists are much different than that of previous lithographic wavelengths. Electrons generated during EUV exposure are demonstrated to be a source of acid production through a process referred to as electron trapping. Density functional theory modeling indicates that it is energetically favorable for the PAG molecule to decompose if an electron is trapped. Low-energy electrons unlikely to produce holes and secondary electrons generate acid indicating electron-PAG interactions are capable to induce decomposition. Additionally, a more easily reduced PAG (i.e. higher likelihood of trapping an electron) produces a higher acid yield supporting electron trapping as a process of acid production. An acid indicator, Coumarin 6, was used to determine the number of acids generated per absorbed EUV photon. The results of these measurements indicate that electron-PAG interactions are a source of acid production through electron trapping; thus, increasing the number of electron-hole pairs available to induce chemical reactions would improve sensitivity. It is expected that lower band gap materials produce more electron-hole pairs after an absorption event. Subsequently, these measurements show that lower band gap polymers generate higher acid yields.
Steven Grzeskowiak, Jake Kaminsky, Sean Gibbons, Michael Murphy, Jonathan Chandonait, Robert L. Brainard, and Greg Denbeaux, "Polymer effects on PAG acid yield in EUV resists," Proc. SPIE 10586, Advances in Patterning Materials and Processes XXXV, 105860D (Presented at SPIE Advanced Lithography: February 27, 2018; Published: 21 March 2018); https://doi.org/10.1117/12.2297692.
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