Analysis of EUV induced depolymerization and side reactions of polyphthalaldehydes for dry develop EUV resist applications

Abstract

With the emergence of extreme ultraviolet (EUV) lithography, poly(phthalaldehyde) (PPA) has regained attention as a potential photoresist four decades after its initial introduction to the field of lithography in the 1980s. The main advantage of PPA is its chemical amplification via spontaneous depolymerization upon exposure to external stimuli such as EUV photons, offering an alternative to acid amplification to increase sensitivity for chain scission resists. Chain scission depolymerization results in the formation of small molecular fragments and monomers that can vaporize making PPA a potential candidate for a dry-developed resist. Dry development, unlike conventional liquid development, prevents the pattern collapse of critical nanometer features by eliminating surface tension forces. However, single-component, end-capped PPA was found to be insensitive to EUV exposure. In this study, cyclic PPA and a copolymer of phthalaldehyde and propanal demonstrated significantly higher EUV sensitivity. However, complete and dry removal was not achieved under the tested conditions. The reason for incomplete film removal via dry development was investigated using spectroscopic and surface analysis techniques including grazing angle Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), and time of flight-secondary ion mass spectroscopy (TOF-SIMS). In this report, the main challenges of dry-develop PPA-based EUV resists are discussed.