Postexposure delay effect in chemically amplified resists

Abstract

Copolymers containing basic monomers such as 3-(t-butoxycarbonyl)-1-vinyl caprolactam (BCVC) and piperidyl 5-norbornene-2-carboxylate (PNC) were synthesized for postexposure delay (PED) stability. The evaporation of a photogenerated acid in a basic polymer film was measured by a spectral change of tetrabromophenol blue sodium salt and the diffusion of the photogenerated acid in the film was investigated using Ficks law and the transport equation of internal diffusion and surface evaporation. As the content of the basic monomer increases in the resist composition, the evaporation and diffusion of the photogenerated acid are reduced since only acids surviving the deactivation by the basic units diffuse and evaporate. Also, the sterically hindered aliphatic basic additive, cis-2,6-di-t-butylpiperidine (DBPi), was synthesized and evaluated for PED stability. With these methods, the control of diffusion and evaporation of the photogenerated acid was accomplished without severe deterioration of the sensitivity. These new resist systems enable us to form fine patterns even after PED under an ammonia atmosphere.