Experimental measurements of electron scattering parameters in Cu narrow lines

Future generations of integrated circuits will require interconnects with metallic lines at dimensions below 50 run. When Cu is used, the electron mean free path becomes similar to the characteristic dimensions of the structure of the metallic line (grain size, interface and wall spacing). This induces a large metal resistivity increase which has a negative impact on the circuit performance. Cu resistivity models have been proposed using the classical Fuchs and Sondheimer approach for surface effect, and the Mayadas and Shatzkes approach for the grain boundary effect (FS-MS approach). In these models, three adjustable parameters must be used. Good agreement between experimental resistivity vs linewidth curves and models can easily be obtained. However, numerous fitting parameter sets can be obtained with equivalent fitting quality and opposite physical meaning. In this work, experiments dedicated to model parameter extraction are proposed and released. They are based on the used of Cu lines with various line widths and heights. Special care is taken in the accuracy of resistivity and dimensions measurements. Classical resistivity increase with line width and line height decrease is observed. Using the FS-MS approach, the observed resistivity behaviour is modelled. In this case, limited fitting parameter options are obtained. For Cu narrow lines confined with Ta, these parameters suggest high surface effect, medium grain boundary effect and low impurity content inside the lines. (c) 2006 Elsevier B.V. All rights reserved.