循环加载下金属薄膜的裂纹萌生行为及其微观机制的研究

金属薄膜广泛应用于大规模集成电路及微机电系统(micro-electro-mechanical systems,MEMS)设备中,循环加载下薄膜的可靠性至关重要.本研究在聚合物基体上制备不同厚度的铜薄膜.研究它们在循环加载下的疲劳裂纹萌生行为及其机制.实验结果表明,薄膜厚度影响薄膜的循环应变局部化和裂纹萌生行为.随薄膜厚度的减小,裂纹萌生从厚薄膜中的挤出诱发的疲劳开裂方式逐步转向较薄薄膜中的界面诱发的疲劳开裂方式.由于基体的约束,位错结构随薄膜厚度的变化是疲劳开裂行为变化的原因.

STUDY OF THE CRACK INITIATION BEHAVIOR AND ITS MECHANISM OF THIN METAL FILMS UNDER CYCLIC LOADING

Thin metal films are widely used in ultra-large scale integrated circuits and microelectromechanical systems (MEMS). The reliability of the metal films under fatigue load is very important. In this study, Cu films were prepared on the polyimide substrates. The fatigue crack initiation behaviour and its mechanism were investigated. The results show that cyclic strain localization and crack initiation behaviour are strongly affected by film thickness. With decreasing film thickness, crack initiation behaviour changes from the extrusion-induced fatigue cracking in the thicker films to the interface-induced fatigue cracking in the thinner films. The transition of the fatigue cracking behaviour is attributed to the change in dislocation structure with film thickness due to the substrate constraint.