Plasticity mechanism for copper extrusion in through-silicon vias for three-dimensional interconnects

Abstract

In this paper, we demonstrated the plasticity mechanism for copper (Cu) extrusion in through-silicon via structures under thermal cycling. The local plasticity was directly observed by synchrotron x-ray micro-diffraction near the top of the via with the amount increasing with the peak temperature. The Cu extrusion was confirmed by Atomic Force Microscopy (AFM) measurements and found to be consistent with the observed Cu plasticity behavior. A simple analytical model elucidated the role of plasticity during thermal cycling, and finite element analyses were carried out to confirm the plasticity mechanism as well as the effect of the via/Si interface. The model predictions were able to account for the via extrusions observed in two types of experiments, with one representing a nearly free sliding interface and the other a strongly bonded interface. Interestingly, the AFM extrusion profiles seemed to contour with the local grain structures near the top of the via, suggesting that the grain structure not only affects the yield strength of the Cu and thus its plasticity but could also be important in controlling the pop-up behavior and the statistics for a large ensemble of vias.

Correlation between Cu microstructure and TSV Cu pumping

“…Measurements and simulations show that most of the plastic deformation during Cu pumping occurs at the TSV top [8,9]. This in part explains why a correlation was found based on the microstructure at the TSV top only, even though this is only a very small part of the overall TSV microstructure.…”

Residual stress preserved in quartz from the San Andreas Fault Observatory at Depth

“…Laue microdiffraction was developed by materials scientists to characterize texture, strain, and stress on a subgrain level (e.g., Chen et al, 2009;Ice et al, 2011;Jiang et al, 2013). Residual stress has been investigated in metals for a long time, documenting lattice distortions through diffraction evidence (e.g., Noyan and Cohen, 1987).…”

Effect of high temperature storage on the stress and reliability of 3D stacked chip

“…The presence of geometrically necessary dislocation (GND) in Cu can cause peak broadening of the Laue reflections [12,13]. The average peak width (APW) obtained in the data analysis provides a measure of the dislocation density and also serves as an indication of plasticity [12,13]. In Figure 4, the APW is plotted for vias in the top die and bottom die before and after HTS.…”

“…This suggests that the grain structure of Cu was rather stable, which is to be expected since the grain structure was stabilized after postplating annealing which is normally carried out at a much higher temperature than that used in the HTS test. The presence of geometrically necessary dislocation (GND) in Cu can cause peak broadening of the Laue reflections [12,13]. The average peak width (APW) obtained in the data analysis provides a measure of the dislocation density and also serves as an indication of plasticity [12,13].…”