Fluorinated copolymer resists for high-resolution negative-tone lithography: Preparation and patterning performance

In response to the increasing demands in advanced lithography for high-resolution and highly stable photoresists, the development of high-performance resist materials has become critically important. In this study, a series of poly (tert-butyl methacrylate-co-adamantyl methacrylate-co-[trifluoroethyl methacrylate/1,1,1,3,3,3-hexafluoroisopropyl isobutyrate methacrylate]) copolymers (PTAF) were rationally designed and synthesized, and their preparation conditions were systematically optimized via a single-factor experimental design. The molecular weight distribution, thermal properties, hydrophobicity, and electron-beam lithography (EBL) performance of the resulting polymers were comprehensively investigated. The results show that PTAF exhibits a narrow molecular weight distribution (polydispersity index = 1.2-1.3) and a number-average molecular weight (M _n ) of approximately 4271 g mol^-1. The polymer demonstrates good thermal stability, with an initial decomposition temperature (T _d) of 212°C and a glass transition temperature (T _g) of 105°C, along with pronounced hydrophobicity. EBL results reveal that PTAF displays intrinsic negative-tone behavior in the absence of externally added photoacid generators, enabling fabrication of high-resolution patterns with a minimum linewidth of 16.5 nm. Mechanistic studies indicate that fluorinated monomers undergo ionization upon irradiation, initiating in situ acid generation, which subsequently triggers the deprotection of tert-butyl ester groups during post-exposure baking. This process leads to a polarity reversal and a corresponding solubility switch in the resist system. Overall, this work establishes a high-performance ternary copolymer photoresist platform and elucidates its negative-tone imaging mechanism, providing valuable insights for the design of polymer-based resists in advanced lithography, particularly for extreme ultraviolet applications.