Application of dual-functional MoO3/WO3 bilayer resists to focused ion beam nanolithography

Ultrafine patterning and metallization technologies have been studied using a combination of refractory metal oxide (MoO3 and WO3) resists and Ga+ focused ion beam lithography. It is demonstrated that, depending on the preparation condition of the films, these thin oxide films act as either a negative or a positive resist with high-contrast capability. As a novel application of this dual-functional behavior, a bilayer resist system using negative (MoO3) and the positive-type (WO3) resists is presented here in order to enhance the high-resolution capability. Based on this technique, nanometer-width MoO3/WO3 line patterns can be delineated onto Si substrates. The delineated line patterns were directly reduced to fine Mo/W wires by heat treatment in a dry H2 gas atmosphere. The electrical properties of the Mo/W lines were evaluated in terms of sheet resistance and their temperature dependence. By introduction of the bilayer resist, the sheet resistance of reduced nanowires was significantly decreased in comparison to that of the monolayer case. The usefulness of oxide resists as refractory metal nanowiring has been further increased by employing the bilayer resist system.