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 WO 3 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/cm 2 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 WO 3 , by ion implantation. The resistive property can thus be explained from the metal transition of Na x WO 3 at the threshold dose.