UC Berkeley

Extreme Ultraviolet Lithography (EUVL) has been introduced to meet the need for smaller feature sizes. EUVL imaging chemistry is revolutionary because of ionizing radiation is involved. Novel physical and chemical processes has made material development more akin to shooting in the dark. In this work, the author delineates the material challenge of EUV photo-sensitization at the molecular level, presents investigations in elucidating sensitization mechanisms and explores new possibilities. The author argues that chemical activation, which connects EUV photon absorption and generation of reactive species, is one of the main driver of resist performance. Three electron spectroscopy techniques are introduced and characterized to interrogate the electron cascade subsequent to photo-ionization. These experiments mainly answer questions about how reactive radical cations and slow electrons are generated. For example, the size of this cascade was found to be between 1 to 4 nanometers in various materials. Once the radical cations are cooled and the slow electrons have attached to electron acceptors, existing computational chemistry techniques are used to understand the subsequent generation of active species. Specifically, photo acid generators (PAG) and a prototypical organo-tin oxo cluster are studied in detail. This study revealed that the said organo-tin oxo cluster reacts to both ionization and electron attachment with similar chemical outcomes, thus partially explaining its superior performance. Manipulating dose by modifying interface dipole is also investigated. Finally, consolidating what he has learned along the way, the author discusses possibilities in EUV material engineering.