Analyses of crack growth along interface of patterned wafer-level Cu–Cu bonds

Abstract

a b s t r a c tA preliminary theoretical study is carried out of the role of micron-scale patterning on the interface toughness of bonded Cu-to-Cu nanometer-scale films. The work is motivated by the experimental studies of [Tadepalli, R., Turner, K.T., Thompson, C.V., 2008b. Effects of patterning on the interface toughness of wafer-level Cu-Cu bonds. Acta Materialia 56, 438-447; Tadepalli, R., Turner, K.T., Thompson, C.V., 2008c. Mixed-mode interface toughness of wafer-level Cu-Cu bonds using asymmetric chevron test. J. Mech. Phys. Solids 56, 707-718.] wherein 400 nm Cu films were deposited in a variety of patterns on Si wafer substrates. Specimens were then produced by bringing the Cu surfaces into contact creating thermocompression bonds. Interface toughness of these specimens was experimentally measured. The present study focuses on interface patterns comprised of bonded strips, called lines, alternating with lines of unbonded interface, all aligned parallel to the crack front. The interface toughness model employs a cohesive zone to represent separation of the interface and J 2 flow theory of plasticity to characterize the Cu films. Remote mode I loading is imposed on the elastic Si substrates. The computational model provides the resistance curve of macroscopic crack driving force versus crack advance as dependent on the work of separation and strength of the interface as well as the pattern geometry and the parameters controlling the plasticity of the Cu films. Plasticity in the Cu films makes a major contribution to the macroscopic interface toughness measured by Tadepalli, Turner and Thompson. Highlighted in this study is the difficulty of accurately representing plastic yielding in the thin films and the challenge of capturing the full range of scales in a computational model.

Quantitative Prediction of Effective Toughness at Random Heterogeneous Interfaces

“…Generally, dissipative processes in the bulk of the solid (yet in the vicinity of the crack surface) contribute to (or even dominates over) the thermodynamic surface energy. This effect has been highlighted in recent studies [17,18] showing how periodic modulations of elastic or interface properties affect crack propagation and considerably enhance the effective toughness of a given interface. Until recently [19][20][21], however, the computation of such an effective macroscopic toughness for random media has remained mostly unexplored despite its great theoretical (critical point of the depinning transition) and practical importance (optimized bonding).…”

Thin films interfacial adhesion characterization by Cross-Sectional Nanoindentation: Application to pad structures

“…Moreover, around the crack tip, the stress field is influenced by the neighboring materials. An interesting numerical study [11] has investigated the effect of the copper ductility on the crack growth in patterned structures. It was clearly shown that the plasticity of the copper increases significantly the crack growth resistance.…”

On the fracture behaviour of CFRP bonded joints under mode I loading: Effect of supporting carrier and interface contamination

“…Potentially, the channelling void may turn the steadystate crack growth into an unstable process. In [37] an array of discrete soldered bands was analysed in two dimensions (2D) within the cohesive zone modelling framework. Effects of the crack front plasticity on interactions between the bands were elucidated.…”