Microscopy and Microanalysis

Materials Applications

Three-Dimensional Measurement of Line Edge Roughness in Copper Wires Using Electron Tomography

Peter Erciusa1 c1, Lynne M. Gignaca2, C.-K. Hua2 and David A. Mullera1

a1 School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA

a2 IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598, USA

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.

(Received September 15 2008)

(Accepted February 10 2009)

Correspondence:

c1 Corresponding author. E-mail: PAE9@cornell.edu