Novel Microtensile Method for Monotonic and Cyclic Testing of Freestanding Copper Thin Films M.-T. Lin & C.-J. Tong & K.-S. Shiu Received: 19 May 2008 / Accepted: 12 January 2009 / Published online: 30 January 2009 # Society for Experimental Mechanics 2009 Abstract This paper presents the results of new micro- tensile tests conducted to investigate the mechanical properties of submicron-thick freestanding copper films. The method, used in this study, allows the observation of materials response under uniaxial tensile loads with measurements of stress at strain rates up to 5.5×10 −4 /s. It also facilitates tension–tension fatigue experiments under a variety of mean stress conditions at cyclic loading frequen- cies to 20 Hz. The sample processes involve fabrication of a supporting frame with springs and alignment beams all made of electroplated nickel. Electroplating took place on top of a previously deposited sample rather than creating a structure by subtractive fabrication. Tensile sample loading is applied using a piezoelectric actuator. Load was measured using a capacitance gap sensor with a novel mechanical coupling to the sample. Tension–tension fatigue experiments were carried out with feedback to give load control. Fatigue tests were conducted on sputter-deposited 500 and 900 nm copper films with grain sizes ∼50 nm. Fatigue life reached 10 5 cycles at low mean load, which decreased with an increase in the mean load. The results indicate decreasing plasticity with increasing mean load. Keywords Stress–strain measurement of copper thin films . Cyclic creep of submicron copper thin films . Microtensile testing . Fatigue testing of Cu thin films Introduction The microelectronics industry has grown rapidly in recent years. The roadmap of microsystems technology calls for increased complexity and packing density of micro-nano scale devices. This allows the fabrication of ever smaller densely packed nanostructures. Continued growth of micro- systems technology requires still further miniaturization. This, in turn, requires an understanding of how length scales affect mechanical behavior. A current goal of MEMS (Microelectromechanical Systems) is to integrate many types of miniature devices onto a single chip for use in a variety of applications. To date, MEMS devices have been generally made using conventional integrated circuit fabri- cation techniques. As in IC technology, materials properties play an important role in MEMS. Recent studies on MEMS fabrication, design, and testing indicate the importance of optimization on their performance. Bulk mechanical failure by fatigue and fracture rarely occurs for MEMS devices which are optimized for design fabrication [1]. Instead, MEMS failure may arise from the degradation of constituent thin films including grain growth and time-independent/ -dependent deformation due to fatigue or creep. Among materials used for microelectronics and MEMS, Cu thin films are one of the most common because of Cu’s favorable electrical and thermal properties [2]. However, the mechanical properties of Cu films, and the cyclic behavior of Cu thin films, in particular, could ultimately limit the corresponding MEMS devices service life. To illustrate this, micro-machined copper thin film resonators require a vacuum package to obtain the highly selective frequency response. However, the resonant frequency is strongly influenced by the size and properties of the thin films. Reliable design parameters, such as mechanical properties become important in reducing process variation, Experimental Mechanics (2010) 50:55–64 DOI 10.1007/s11340-009-9221-1 M.-T. Lin (*, SEM Member) : C.-J. Tong : K.-S. Shiu Institute of Precision Engineering, National Chung Hsing University, Taichung 402 Taiwan, Republic of China e-mail: mingtlin@nchu.edu.tw