Solid state NMR investigation of photoresist molecular glasses including blend behavior with a photoacid generator

Abstract

We have examined four molecular glass (MG) materials that show promise as photoresists for extreme-ultraviolet (EUV) lithography. These glass-forming materials were investigated by proton and ¹³C solid state nuclear magnetic resonance (NMR) techniques in the bulk state as pure materials and as mixtures with (5 or 10) % by mass of the photoacid generator (PAG), triphenylsulfonium perfluorobutanesulfonate. The ¹³C techniques gave information about crystallinity, purity, and the qualitative existence of multiple phases. Proton studies focused on using spin diffusion to characterize the intimacy of mixing of the PAG and MG blends. The four MGs were largely aromatic materials containing several hydroxyl groups that were partially protected by t-butoxycarbonyl (t-BOC) groups. In two cases, this fraction was varied and the impact on mixing noted. Phase separation of the PAG into PAG-rich larger domains was never seen; the PAG was always finely distributed and the maximum size for any PAG clustering was estimated; however, in some cases, the average local concentration of PAG appeared to vary. Crystallinity was only seen associated with the underivatized materials implying that the mixing of the PAG with any derivatized MG was not restricted by crystallization. It was also noted that some very strong hydrogen bonds exist in three of the four underivatized materials and were eliminated or weakened upon partial derivatization with t-BOC.