Mechanism of a High-Contrast Inorganic Ion Resist Using Amorphous WO3

Abstract

Optical absorption spectra of thin amorphous WO₃ films irradiated by a beam of sodium ions at ∼ 10 kV have been measured in order to determine the properties of these films as a negative-type ion resist. A characteristic color band of amorphous tungsten bronze was observed in a relatively low-dose region. The resist behavior at the threshold dose D _th was linked with the appearance of a metallic luster at the film surface and with a corresponding change in the spectral shape. The surface sodium content at D _th was nearly equal to the value at the insulator-metal transition of sodium tungsten bronze. The mechanism of this inorganic resist is based on a change in the chemical potential; this is mainly due to doping effects by ion implantation and partly due to some structural change by energy deposition.