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

Abstract 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.