Crack progression and interface debonding in brittle/ductile nanoscale multilayers
- PDF / 1,815,285 Bytes
- 11 Pages / 576 x 792 pts Page_size
- 45 Downloads / 203 Views
Crack initiation and progression have been studied in nanoscale brittle/ductile multilayers of Cu and Si. Variations in the interface debond energy on the cracking behavior have been examined by using thin interlayers comprising either Cr (strong interface) or Au (weak interface). For strongly bonded Cr interfaces, it has been found that cracks forming in the Si invariably extend through the Cu layers, despite the ductile rupture characteristics of the Cu. This behavior occurs even when the Cu layers comprise more than 70% of the multilayer volume. It also contrasts with the crack arrest capabilities exhibited by relatively thick ductile layers (—10-100 /xm). The disparity in behavior is attributed to the relatively large cracking strain required for the thin brittle layers. Weak Au interfaces result in debonding which, in turn, can suppress the propagation of cracks into adjacent layers. However, when the interface includes strongly bonded sections, the debond arrests, and often kinks into the attached Si. In this case, cracking still progresses sequentially through the Si layers. Careful control of the interface debond energy is needed to fully suppress crack progression in nanoscale multilayers.
I. INTRODUCTION Multilayers that contain a mix of brittle and ductile materials have applications in electronic devices, electronic packaging, and multilayers.'~3 The brittle materials of interest include Si, as well as various oxides and nitrides. The ductile materials include Al, Cu, Ni, and Au.4 Upon subjection to stresses, which arise from a combination of applied loads, thermal expansion, and intrinsic misfit, the brittle layers may microcrack and the interfaces may debond, or both.3-5"8 Such damage often degrades the performance and reliability of the multilayer. A particularly deleterious mode of damage arises when the initial microcrack that forms in one of the brittle layers communicates with the next brittle layer, leading to the formation of a dominant macrocrack. The conditions that induce this response have been examined for relatively thick (100-1000/^m) layers of A12O3 bonded to either Al or Cu.9 The intent of the present study is to establish the corresponding characteristics when the layers are thin, in the 50-500 nm range, where different phenomena might be expected.4 The studies performed on the thick layers have established that the role of a well-bonded ductile layer between two brittle layers is simply to arrest the cracks that first form in one of the brittle layers.9"13 The plastic deformation of the ductile layer, surprisingly, has minimal influence on the stress concentration in the next brittle layer. In fact, reasonable estimates of this stress concentration can be obtained from the elastic solution for a homogeneous solid. 912 In consequence, it 1958 http://journals.cambridge.org
J. Mater. Res., Vol. 10, No. 8, Aug 1995 Downloaded: 18 Mar 2015
has been found that the relative thickness of the ductile layer must be quite large in order to negate the stress concentration. Typically, the volu
Data Loading...
