Structural Change In a Inorganic Resist From Peroxopolytungstic Acid During Deep-UV Irradiation

Abstract

Peroxopolytungstic acid (W-IPA) is a promising inorganic resist material formed by a direct reaction of metallic tungsten and hydrogen peroxide. Thin films about O.5 pm thick were formed on silicon wafer or glass substrate by conventional spin coating technique using its 50 wt% aqueous solution. Its structural change during UV irradiation, which makes the films insoluble in water, was evaluated by IR, Raman and RDF (radial distribution function)and compared to that brought about by heat treatment. Infrared and Raman spectroscopy revealed that an edge-sharing arrangement of the WOG octahedra (or W07 pseudo-octahedra)in W-IPA disappeared after heating it over 100 °C, while the structure remained substantially unchanged when it was heated at 80 °C for as long as 8 h. Such an edge-sharing arangement was also destroyed by UV-irradiation up to 4.5 J cm-2. After irradiation, W-IPA film was changed into a dense structure built up of corner-sharing WOG octahera, which was generated by the condensation of polyaninons accompanied with the decomposition of their peroxo ligands. The resultant oxygen molecules were caged in such a network structure at least partly and retained until structural rearrangement or crystallization.