Ultafine Lithography by Oxide Ion Resists and Its Applications.

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(1) Microlithographic PropertiesThin amorphous films of WO_3, MoO_3, V_2O_5 and a mixture theirof were formed on Si wafers and exposed to a 20-70 keV Ga^+ FIB. Development after writing was performed by chemical etching. The basic properties of these films as an inorganic resist were evaluated in terms of the resist sensitivity, the contrast, the dry etching durability of the delineated resist patterns and the selectivity with respect to Si. The details of the characteristics can be explained from the physical and chemical properties of the resist material.(2) Resist Mechanism and Limiting ResolutionThe resist mechanism was made clear by the analyses of the exposure characteristics, surface analyses of the exposed films and the electrical measurement. Studies of line exposure and measurements of the beam profile of the FIB indicate that the limiting resolution of this resist work is determined by the FIB diameter, owing to its high contrast capability.(3) Application StudiesThin amorphous films of MoO_3 were deposited by electron beam evaporation onto Si wafers, and were exposed to 30-50 keV Ga^+ FIB. Fine line patterns of MoO_3, developed by chemical etching after line exposure, were reduced to Mo by heat treatment in H_2 atmosphere. From measurements of the line width before and after reduction as a function of the ion dose, it was demonstrated that 50-100 nm width fine patterns of Mo can be formed on Si substrates. This technique is potentially useful for fabrication of lowerーsubmicron devices, quantum wire and X-ray mask.