Chemically enhanced focused ion beam micromachining of thin film Cu on Si substrates has been investigated. Barrier layers and dielectric layers were considered as well. The gases investigated include the Cl containing examples Of C2Cl4, C2H4Cl2, and CHCl2CCl3 as well as the oxygen containing gases ethanol, and methanol and water vapor. Crystallographic channeling effect results in nonuniform Cu milling, insufficient selectivity and poor end-point detection. However, the gases investigated were shown to enhance the milling homogeneity, improve the end-point detection, and provide higher selectivity. A Cu/SiO2 selectivity of greater than 4 was obtained when using ethanol as the etching gas.