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2011
Conference Paper
Titel
Nanoindentation study of elastic anisotropy of Cu single crystals and grains in TSVs
Abstract
This paper presents the results of nanoindentation experiments on Cu single crystals and Cu grains in through silicon via (TSV) structures used for 3D integrated circuit (IC) stacking, at sub-10nm and several-10nm penetration depths. The reduced moduli for Cu single crystals change from an average value to the uni-directional values, as the penetration depths decrease from several-10nm to sub-10nm. At sub-10nm deformation, about one third of the indentations on Cu(111) and Cu(110) show fully elastic behavior, while all indentations on Cu(100) shows elastic-plastic behavior. The reduced modulus values extracted from indents on Cu(111) and Cu(110) with fully elastic behavior are about 195GPa and 145GPa, respectively. For penetration depths of several-10nm up to 50nm, the reduced modulus for Cu(100) varies between 50GPa to 100GPa. The averaged reduced moduli determined at relatively large penetration depths are explained with lattice rotation beneath the indentations. Sinc e the activation of multiple slip systems is required for lattice rotation, the transition of the unidirectional reduced modulus to the averaged value with increasing penetration depths occurs differently for Cu(111) and Cu(100). Similar to the results from Cu single crystals, unidirectional reduced moduli are obtained for the Cu grains in TSV structures at sub-10nm penetration depths.