Focused ion beam fabrication of submicron gold structures

Abstract

Because of their ability to both mill and deposit material with submicron resolution, focused ion beams are now used to repair photolithography masks and are of increasing technological interest in the repair of x-ray lithography masks and in integrated circuit restructuring. With the latter two applications in mind, we have fabricated milled and deposited Au features with linewidths of ≤0.1 μm using a 40 keV Ga focused ion beam. In addition, we present the results of a study parameterizing focused ion beam induced Au deposition under conditions of practical interest. Milling is accomplished by simple physical sputtering. Examples of milled microfeatures include a grating with a 210 nm period milled through a 5000 Å thick evaporated Au film. Deposition is accomplished by ion bombarding a SiO2 substrate on which a precursor gas, dimethyl gold hexafluoro acetylacetonate, is continuously being adsorbed. Examples of deposited Au features include a 3×3 μm patch 1-μm-thick with steep sidewalls. The deposition rate was measured at room temperature as a function of ion and precursor flux, and a simple model of the process is fitted to the data. Ion beam induced deposition efficiency is shown to depend critically on the time averaged beam current density and only weakly on the precursor flux. The maximum achievable growth rate is shown to be ∼10 Å/s. Deposited Au films contain 30–60 at. % carbon and have conductivities 200–600 times less than that of bulk Au. Those films formed using lower organometallic pressures or higher ion beam current densities are characterized by greater purity with more continuous microstructure.