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‐10 nm and several‐10 nm 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‐10 nm to sub‐10 nm. At sub‐10 nm 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 195 GPa and 145 GPa, respectively. For penetration depths of several‐10 nm up to 50 nm, the reduced modulus for Cu(100) varies between 50 GPa to 100 GPa. The averaged reduced moduli determined at relatively large penetration depths are explained with lattice rotation beneath the indentations. Since 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‐10 nm penetration depths.