Study of CF4 gas based dry development for vertically structured organic-inorganic multilayer EUV photoresist

Abstract

Study of CF4 gas based dry development for vertically structured organic-inorganic multilayer EUV photoresist Jiwoo Jung Division of materials Science and Engineering Graduate School of Hanyang University Supervised by Prof. Jinho Ahn Extreme ultraviolet lithography (EUVL) is recognized as a pivotal technology for achieving high semiconductor integration, particularly with the ongoing development of sub-nanometer ultra-fine patterns. However, existing photoresist (PR) materials and processes encounter several limitations in realizing high-performance fine patterns. To address these challenges, continuous research is being conducted on novel forms of EUV photoresist materials and processes. In this study, we introduce a novel dry development process for a vertically structured organic-inorganic multilayer EUV photoresist, deposited by Molecular Layer Deposition (MLD). The conventional wet development process confronts critical issues, such as pattern deformation and collapse in sub-nanometer-scale patterns, attributed to high aspect ratios and capillary effects of the aqueous developer. To overcome these challenges, a dry development process utilizing plasma generated by the Reactive Ion Etching (RIE) technique is introduced. The dry development process experiments analyzed the behavior of a negative-tone EUV photoresist with various process gas types. After understanding the role and mechanism of each gas to achieve high development degree and selectivity ratio patterns, it was determined that CF4/O2 gas conditions were optimal. Furthermore, attention was drawn to the differences between wet and dry development processes, investigating the cause of high surface roughness in the dry development process. In the wet development process, liquid-state developers are used to rinse and remove the unexposed area, while in the dry development process, radicals and ions in the plasma react with the photoresist and also the substrate simultaneously, resulting in high surface roughness. Experimental confirmation of the difference in surface roughness after each process was conducted to identify this phenomenon. To address the cause of high surface roughness in the dry development process, experiments were conducted to examine the reaction conditions between the process gas and the substrate. The results revealed that the SiO2 substrate exhibited active reactions with the applied CF4 process gas, whereas the introduction of an Al2O3 substrate, unresponsive to CF4 gas, led to a significant reduction in surface roughness. This outcome the penetration of fine gas particles into the photoresist, triggering reactions with the substrate during the dry development process, causing high surface roughness. This research validates the potential of the newly introduced dry development process, which utilizes plasma for the EUV photoresist. Moreover, the significance of the relationship between the substrate and process gas during the dry development process is highlighted through experimental confirmation. Through this, it is anticipated that the newly proposed dry development process will contribute to the performance enhancement of vertically structured organic-inorganic hybrid EUV photoresist.