Visualization of organic/inorganic hybridization of UV-cured films with trimethylaluminum by scanning transmission electron microscopy and energy dispersive x-ray spectroscopy

The organic/inorganic hybridization of photopolymerized resist films for ultraviolet nanoimprint lithography (UV-NIL) through chemical vapor modifications of atomic layer deposition (ALD), sequential infiltration synthesis (SIS), and saturated vapor infiltration (SVI) with an inorganic precursor of trimethylaluminum (TMA) and an oxidant of water was investigated. The hybridization of the bisphenol A-based polymethacrylate resist films was compared between resin-A comprising a monomer with hydroxy groups and resin-B comprising another monomer without hydroxy groups. The elemental depth profiles by scanning transmission electron microscopy and energy dispersive x-ray spectroscopy revealed the following three things. ALD and SIS caused the hybridization of the organic resist films with inorganic alumina near the film surfaces, while SVI caused the hybridization of the resist films entirely. The hydroxy-free resin-B physically adsorbed and chemically fixed more TMA molecules than the hydroxy-containing resin-A. Although SIS progressed the entire hybridization of the resist films, different behaviors of segregation of alumina between the hydroxy-containing resin-A and hydroxy-free resin-B films were confirmed near the film surface, inside, and interface with a silicon substrate. The organic/inorganic hybridization enabled the tuning of the etching rate of the NIL resist masks with a thickness of no thicker than 20 nm in oxygen reactive ion etching often used for the removal of residual layers from imprint patterns in UV-NIL processes.