Direct detection of grain boundary scattering in damascene Cu wires by nanoscale four-point probe resistance measurements

Four-terminal conductivity measurements of damascene copper (Cu) wires with various widths have been performed using platinum-coated carbon nanotube (CNT) tips in a four-tip scanning tunneling microscope. Using CNT tips enabled the probe spacing to be reduced to 70 nm, which is the shortest probe spacing in interconnect wire measurements achieved so far. The measured resistivity of Cu increased as the line width decreased and direct evidence of individual grain boundary scattering was observed when the probe spacing was varied on a scale comparable to the grain size of the Cu wires (∼200 nm).