Fluorinated acid amplifiers for extreme ultraviolet lithography

Abstract

Extreme ultraviolet lithography (EUV) is a promising candidate for next generation lithography. Although EUV has great potential there are still many challenges that must be solved before the technology can be implemented in the high volume manufacturing of semiconductor devices. The lithographic performance of EUV photoresists is one aspect that requires improvement. Particularly, EUV resists need simultaneous improvements in three properties: resolution, line-edge-roughness and sensitivity. The incorporation of acid amplifiers (AAs) in resists is one method to improve all three properties.

Acid amplifiers are compounds that decompose via acid-catalysis to generate more acid. Successful AAs must be thermally stable in resist films under normal resist process conditions and they must generate strong fluorinated sulfonic acids. To the best of our knowledge, there are only 29 AAs published in the literature prior to our work on this topic, none of which meet the requirements for use in EUV resists.

This thesis describes the synthesis and characterization of new AAs specifically designed for EUV resists. More than 40 new AAs were synthesized. The compounds were lithographically evaluated in EUV resists. Decomposition reaction kinetics were measured using ¹⁹F NMR spectroscopy. Investigations were done to measure AAs: thermal stabilities in resist films, acid generation in resist films, decomposition products, and species outgassed from resist films exposed to EUV light. A model was developed to predict AAs effects on acid gradients in resist films and on resists sensitivities. The last chapter shows some preliminary results of AAs that have record thermal stabilities and that generate triflic acid.