Mixed-mode interface toughness of wafer-level Cu–Cu bonds using asymmetric chevron test

Tadepalli, Rajappa; Turner, Kevin T.; Thompson, Carl V.

doi:10.1016/j.jmps.2007.07.016

Cited by 22 publications

(15 citation statements)

References 24 publications

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“…Several studies on Cu-Cu thermocompression bonding have been reported, varying bonding process parameters such as the Cu surface quality, bonding temperature, applied pressure, and postannealing conditions. [10][11][12] However, there has been little quantitative adhesion study of chemical surface treatment effects.…”

Section: Introductionmentioning

confidence: 99%

Effect of Wet Pretreatment on Interfacial Adhesion Energy of Cu-Cu Thermocompression Bond for 3D IC Packages

Jang

Hyun

Lee

et al. 2009

Journal of Elec Materi

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Quantitative analysis of the interfacial adhesion energy of Cu-Cu thermocompression bonds was performed using the four-point bending method with various wet pretreatment conditions. The evaluated interfacial adhesion energies for 1-lm-thick Cu bonding layers were 0.29 J/m 2 , 1.28 J/m 2 , 1.64 J/m 2 , 1.17 J/m 2 , and 0.43 J/m 2 for different acetic acid pretreatment times of 0 min, 1 min, 5 min, 10 min, and 15 min, respectively. There exists an optimum wet etch time for maximum adhesion strength. The change of surface properties with increasing wet etch time was believed to result in the variation of the interfacial adhesion energy. The decrease in interfacial adhesion energy after 5 min seems to result from a decrease in the plastic dissipation energy during interfacial crack propagation with thinner Cu film thickness caused by overetching.

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Section: Introductionmentioning

confidence: 99%

Effect of Wet Pretreatment on Interfacial Adhesion Energy of Cu-Cu Thermocompression Bond for 3D IC Packages

Jang

Hyun

Lee

et al. 2009

Journal of Elec Materi

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“…This mechanism has been used to evaluate the interfacial shear strength (Agrawal and Raj 1989) and to measure the elastic modulus and the fracture toughness of the film (Thouless et al 1992;Wang et al 1998). A number of experiments have been developed to study the dependence of fracture behavior on the geometry of the film, the mechanical properties of the film and substrate, and conditions of the interface (see, for example, Hu and Evans 1989;Bordet et al 1998;Etzkorn and Clarke 2001;Alaca et al 2002;Zhao et al 2002;Malzbender 2004;Tadepalli et al 2008). Fig.…”

Section: Introductionmentioning

confidence: 99%

An explicit elastic solution for a brittle film with periodic cracks

2008

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A two-dimensional explicit elastic solution is derived for a brittle film bonded to a ductile substrate through either a frictional interface or a fully bonded interface, in which periodically distributed discontinuities are formed within the film due to the applied tensile stress in the substrate and consideration of a "weak form stress boundary condition" at the crack surface. This solution is applied to calculate the energy release rate of three-dimensional channeling cracks. Fracture toughness and nominal tensile strength of the film are obtained through the relation between crack spacing and tensile strain in the substrate. Comparisons of this solution with finite element simulations show that the proposed model provides an accurate solution for the film/substrate system with a frictional interface; whereas for a fully bonded interface it produces a good prediction only when the substrate is not overly compliant or when the crack spacing is large compared with the thickness of the film. If the section is idealized as infinitely long, this solution in terms of the energy release rate recovers Beuth's exact solution for a fully cracked film bonded to a semi-infinite substrate. Interfacial shear stress and the edge effect on the energy release rate of an asymmetric crack are analyzed. Fracture toughness and crack spacing are calculated and are in good agreement with available experiments.

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“…Because that the plastic zone size is R P ffi ðG=C 0 ÞR 0 , it seems likely that the plastic zone is on the order of the film thickness during crack propagation in the specimens of Tadepalli et al, especially for the toughest interfaces. Tadepalli et al (2008c) have shown SEM micrographs and AFM images of Cu-Cu fracture surfaces to illustrate that the fracture surfaces are much rougher under mixed-mode loading where plasticity plays a larger role. This effect of plasticity is also illustrated in (Tadepalli et al, 2008b) by SEM micrographs for sufficiently small pattern size of orthogonal lines or pads.…”

Section: Discussionmentioning

confidence: 99%

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

Tvergaard

Hutchinson

2009

International Journal of Solids and Structures

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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.

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Mixed-mode interface toughness of wafer-level Cu–Cu bonds using asymmetric chevron test

Cited by 22 publications

References 24 publications

Effect of Wet Pretreatment on Interfacial Adhesion Energy of Cu-Cu Thermocompression Bond for 3D IC Packages

Effect of Wet Pretreatment on Interfacial Adhesion Energy of Cu-Cu Thermocompression Bond for 3D IC Packages

An explicit elastic solution for a brittle film with periodic cracks

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

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