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Prediction of delamination strength at interface between thin film and substrate by cohesive zone model

This paper aims to predict the delamination strength at the interface edge with arbitrary shape using a cohesive zone model. Two different experiments are conducted for a gold thin film on a silicon substrate to calibrate the cohesive law. The validity of the approach is then discussed. | Vietnam Journa l of Mechanics, VAST, Vol. 28, No. 4 (2006), pp. 252 - 262 PREDICTION OF DELAMINATION STRENGTH AT INTERFACE BETWEEN THIN FILM A ND SUBSTRATE BY COHESIVE ZONE M ODEL Do 1 VAN TRUONG 1 •2 , HIROYUKI HIRAKATA 1 AND TAKAYUKI KITAM URA 1 Department of Engineering Physics and Mechanics, Kyoto University, Japan 2 Department of Design of Machinery 8 Robot, Hanoi University of Technology, Vi etnam Email: dovantruong@yahoo.com Abstract . An electronic device consists of multi-layered submicron-thick films, and delamination often takes place at an interface edge because of the stress singularity near the edge. Since t he stress singularity at an interface edge depends on the edge shape, the fracture mechanics concept cannot be used to compare the delamination strength between the components with different shapes. This paper a ims to predict the delamination strength at the interface edge with arbitrary shape using a cohesive zone model. Two different experiments are conducted for a gold thin film on a silicon substrate to calibrate the cohesive law . The validity of the approach is then discussed . 1. INTRODUCTION Delamination is one of the mechanical fai lures often met in microelectronic devices and it sometimes brings about fatal malfunction of the system. Therefore, the quantitative comparison of interface strength betw~en bi-materials of different combinations is a necessary task to choose the suitable materials and improve the reliability of the devices . In terms of mechanical strength, delamination is mainly caused by the concentrated stress near the interface edge due to the mismatch of the elastic property. According to Bogy [l], the stress field near the interface edge is expressed by the following equation K er = r>- (1.1) here, K is the stress intensity parameter, r is the distance from the edge and ,\ is the stress singularity. Crack initiation is governed by the singular stress field and the strength is characterized by K [2-5]. T he .