Dry‐Develop Positive‐Tone Poly(aldehyde) Resists Activated by Low‐Voltage Electron‐Beam Exposure

ABSTRACT

Dry‐develop positive‐tone resists are attractive for advanced lithographic applications because they eliminate the need for liquid development. Poly(phthalaldehyde) (PPA) is a promising dry‐developable resist platform because acid‐triggered depolymerization converts the polymer to volatile o ‐phthalaldehyde ( o PA), enabling spontaneous or vacuum‐assisted material removal. Here, low‐voltage electron‐beam activation of photoacid‐generator/poly(aldehyde) films was investigated for positive‐tone dry development. PPA films containing diaryliodonium photoacid generators (PAGs) were exposed using a 2 keV scanning electron microscope, and showed exceptionally high sensitivity with the volatile depolymerization products removed under vacuum. Among the PAGs investigated, diphenyliodonium hexafluoroarsenate (DIHA) produced greater mass loss at lower electron‐beam doses than bis(4‐tert‐butylphenyl)iodonium triflate (BIT) or Rhodorsil FABA under the same molar loading conditions. DIHA loading studies showed that the remaining residue thickness, which is primarily due to non‐volatile DIHA products, was reduced by lowering the DIHA concentration. Electron‐beam depolymerization of cyclic poly(propanal‐co‐phthalaldehyde) (PPCP) was investigated to evaluate the effect of depolymerization product volatility. DIHA/PPCP films showed greater thickness loss and cleaner exposed regions than DIHA/PPA films under the same exposure and vacuum‐hold conditions.