CoSi2 structures were formed by focused ion-beam implantation. Patterned silicide lines with dimensions down to 150 nm were produced on (100) silicon. The process involved the ion implantation of 200 keV As++ through a cobalt (34 nm)/oxide (∼2 nm) thin film structure. The thin oxide at the Si/Co interface acted as a selective reaction barrier. Ion-beam mixing disrupted the oxide layer to allow silicidation to proceed during subsequent rapid thermal anneal treatments. Reactions were inhibited in nonimplanted areas. A threshold dose of 3×1015 cm-2 was required for process initiation. Electrical measurements resulted in resistivities ranging from 15 to 30 μΩ cm. © 2001 American Institute of Physics.