title: Three-dimensional measurement of line edge roughness in copper wires using electron tomography.
abstract: Electrical interconnects in integrated circuits have shrunk to sizes in the range of 20-100 nm. Accurate measurements of the dimensions of these nanowires are essential for identifying the dominant electron scattering mechanisms affecting wire resistivity as they continue to shrink. We report a systematic study of the effect of line edge roughness on the apparent cross-sectional area of 90 nm Cu wires with a TaN/Ta barrier measured by conventional two-dimensional projection imaging and three-dimensional electron tomography. Discrepancies in area measurements due to the overlap of defects along the wire's length lead to a 5% difference in the resistivities predicted by the two methods. Tomography of thick cross sections is shown to give a more accurate representation of the original structure and allows more efficient sampling of the wire's cross-sectional area. The effect of roughness on measurements from projection images is minimized for cross-section thicknesses less than 50 nm, or approximately half the spatial frequency of the roughness variations along the length of the investigated wires.
authors.affiliation: School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA. PAE9@cornell.edu
authors.forename: Peter
authors.initials: P
authors.lastname: Ercius
authors.forename: Lynne M
authors.initials: LM
authors.lastname: Gignac
authors.forename: C-K
authors.initials: CK
authors.lastname: Hu
authors.forename: David A
authors.initials: DA
authors.lastname: Muller