Preparation of Hot Water-Resistant Silica Thin Films from Polysilazane Solution at Room Temperature

Abstract

Perhydropolysilazane (PHPS) films were deposited on single-crystal Si substrates by spin-coating using a xylene solution of PHPS, and then suspended over 1 mol L⁻¹ ammonia water at room temperature. The PHPS-to-silica conversion occurring on the exposure to the ammonia water vapor was studied by infrared absorption spectroscopy. Si--H and N--H infrared absorption peaks decreased and Si--O--Si bands increased, showing PHPS-to-silica conversion; the conversion was almost completed in 6 h. The exposed films were soaked in 80°C water for 24 h, and the reduction in thickness on soaking was evaluated. The PHPS-derived films suspended over the ammonia water for 6 h exhibited only 2% reduction in thickness on soaking in 80°C water. Alkoxide-derived silica gel films dried in the ambient atmosphere or suspended over the ammonia water, on the other hand, exhibited significant reduction in thickness on soaking in 80°C water.