Paper EM-TuA7
High Throughput Crystal Orientation Mapping of Nanometric Cu: Impact of Surface and Grain Boundary Scattering on Electrical Resistivity

Tuesday, October 30, 2012, 4:00 pm, Room 009

Due to limitations in characterizing twin boundaries in nanocrystalline Cu, it has been difficult to account for twin boundary scattering in the quantitative analysis of the resistivity size effect. In this study, a recently developed high throughput electron diffraction based metrology method in the transmission electron microscope, known as ASTAR^TM, is employed to obtain crystal orientation maps in two SiO₂ and 6 SiO₂/Ta₃₈Si₁₄N₄₈ encapsulated nanocrystalline Cu thin films. In ASTAR™, a dedicated hardware unit is used for precession and automated scanning of a nanosized quasi-parallel electron beam probe. A high speed external optical camera is then used for rapid acquisition of spot diffraction patterns. The acquired spot patterns are indexed automatically using a template matching algorithm. Significant improvement in the reliability of the orientation maps is achieved with electron beam precession. The use of precession reduces the dynamical effects and increases the number of spots in the diffraction pattern. The use of rapidly acquired spot patterns and the robust template matching algorithm make ASTAR™ highly suitable for obtaining large datasets of crystal orientations. Analysis of the orientation maps of the Cu films shows a significant fraction of incoherent twin boundaries, indicating a potentially higher resistivity contribution from twin boundary scattering than previously assumed. Including the mixture of coherent and incoherent twin boundaries in the study of the resistivity size effect shows that the contribution from grain boundary scattering is still the dominant resistivity size effect in Cu, compared to surface scattering. Inclusion of the twin boundary mixture in a quantitative model shows the resistivity data to be best described by the Fuchs Sondheimer surface scattering model and the Mayadas Shatzkes grain boundary scattering model, combined using Matthiessen's rule (simple summation), with a surface specularity coefficient, p = 0.50, and a grain boundary reflection coefficient, R = 0.26. These values can be compared with values of p = 0.52 and R = 0.43 obtained in previous studies where the presence of twin boundaries was not considered. The potential to separately quantify electron scattering at twin boundaries and non-twin grain boundaries, the role of surface roughness, measured by x-ray reflectivity using synchrotron radiation, and the role of voids, measured using high angle annular dark field imaging in the transmission electron microscope, will also be discussed.