Ion-Beam Modification of Amorphous WO3 Film and Its Properties as a High-Contrast Inorganic Ion Resist

Abstract

The effect of ion-beam irradiation on amorphous WO₃ films was studied experimentally and in detail using thermionic Na⁺ ions with an accelerating voltage of 4∼12 kV. The films exhibit a resistive property of extremely high contrast (γ≃8) at ion doses beyond a threshold value D _th. The sensitivity (D _th ≃5 ×10^-4 C/cm² at 5 kV), which is almost independent of the film thickness, decreases gradually with increasing accelerating voltage. The behavior of the optical absorption spectra and the ion-induced secondary electron emission yield of the irradiated films suggests the formation of sodium tungsten bronze, Na _x WO₃, by ion implantation. The resistive property can thus be explained from the metal transition of Na _x WO₃ at the threshold dose.