AVS 46th International Symposium
    Electronic Materials and Processing Division Thursday Sessions
       Session EM1-ThM

Paper EM1-ThM1
Strength of Nanoscale Copper Under Shear

Thursday, October 28, 1999, 8:20 am, Room 608

Session: Cu, Low-k Dielectrics and Interfaces
Presenter: E. Ristolainen, Tampere University of Technology, Finland
Authors: P. Heino, Tampere University of Technology, Finland
P.H. Holloway, University of Florida
E. Ristolainen, Tampere University of Technology, Finland
Correspondent: Click to Email
Since 1995 when IBM proposed that copper can be used in electrical interconnections, its properties have received a lot of interest in the electronics community, mainly because of its low electrical resistance. Previously we have shown by comparison with experimental data that mechanical properties of copper can be well described using the effective-medium theory (EMT), molecular dynamics simulations, and more than 100k atoms.@footnote 1@ Here we use these methods to study thermally induced shear strain and stress in several nanoscale copper systems consisting of about 200k atoms. The shear strain in the system is generated by moving the top and bottommost boundaries, corresponding to a common deformation mechanism in flip chip interconnect.@footnote 2@ Plastic deformation mechanisms, stress concentration and stress relaxation were studied. The role of microstructure of the system was analyzed. We studied three monocrystalline systems and several polycrystalline structures, in which the grain size was varied. The results show that the strength of the system decreases with decreasing grain size. This is contrary to macroscale behavior, but has recently been found in similar systems under tension. The reason behind this behavior is the soft grain boundary and grain boundary sliding. The strength of the small systems can decrease by a factor of ten, when the structure changes from monocrystalline to polycrystalline. In monocrystalline structures we studied dislocation formation. The results showed that dislocations prefer to initiate at the compressive side of the system rather than at the tensile side. This peculiar behavior could be exlained with the stacking fault energy and its dependence on the state of strain in the context of EMT. More details will be discussed. @FootnoteText@ @footnote 1@P. Heino, H. Häkkinen and K. Kaski: Europhysics Letters 41 (3) 278 (1998) @footnote 2@P. Heino and E. Ristolainen: Proc. Second Int. Conf. on Modeling and Simulation of Microsystems, Apr. 19-21 (1999), San Juan, PR, USA.