Direct writing of iridium lines with a focused ion beam

Abstract

Direct writing of metal features narrower than 100 nm is accomplished by scanning a focused ion beam over a substrate covered with a thin solid metalorganic film. A metalorganic cluster coordination compound [Ir₄(CO)₁₁Br][N(C₂H₅)₄] is spun on an oxidized silicon wafer from acetone solution and the resulting layer is irradiated with a focused 20 keV Ga‐ion beam. The partially decomposed irradiated film regions show a marked decrease of solubility in acetone. Developing by dissolving the nonirradiated parts of the surface hence leaves narrow lines of partially reacted metalorganic precursor. High temperature treatment of these lines, either in vacuum or in a reactive gas stream, completes the decomposition to quite pure iridium, as is confirmed by micro‐Auger analysis. In these preliminary experiments we obtained lines with room temperature electrical resistivities as low as 400 μΩ cm, at direct writing speeds of 40 μm s⁻¹ to 0.8 mm s⁻¹, which correspond to ion doses of 3.1×10¹⁶ ions/cm² to 1.6×10¹⁵ ions/cm², respectively. The width of the metal lines decreases with decreasing ion dose in this range from 180 down to 90 nm. The adhesion to the substrate increases with increasing ion dose. The thickness of the resulting iridium lines depends mainly on the thickness of the metalorganic precursor layer. The maximum possible thickness of the [Ir₄(CO)₁₁Br][N(C₂H₅)₄] layer that can be used depends on the effective penetration depth of the ions in this layer.