Chapter 8 In Situ Energy Loss and Internal Friction Measurement of Nanocrystalline Copper Thin Films Under Different Temperature Yu-Ting Wang, Yun-Fu Shieh, Chien-hua Chen, Cheng-hua Lu, Ya-Chi Cheng, Chung-Lin Wu, and Ming-Tzer Lin Abstract This study uses a temperature controlled capacitance-based system to measure the mechanical behaviors associated with temperature dependent energy loss in ultra-thin copper films. Copper thin films are widely used in electronic interconnections and MEMS structures; however, most studies have focused on their temperature dependent dynamic properties at larger scales. This study designed a paddle-like test specimen with Cu films deposited on the upper surface in order to investigate the in-situ temperature dependent mechanical properties of metal thin films at higher temperature up to 120 C under high vacuum conditions at very small scales. In-Situ Energy loss was measured according to decay in the oscillation amplitude of a vibrating structure following resonant excitation. The results indicated very tight temperature dependent internal friction of ultra-thin Cu metal films. Keywords Internal friction • Energy loss • Ultra-thin Cu thin film • Temperature dependence 8.1 Introduction Thin metal films are widely used in the manufacturing and packaging of microelectronics. Thin metal films applied in ICs and MEMS structures are stacked layer upon layer and are often connected directly to one another. Each step in the process of fabrication may involve a different temperature, which subjects the entire structure to fluctuations in temperature throughout the process. Regardless of whether processing temperatures are raised or dropped, these fluctuations introduce mechanical stress resulting from the mismatch in thermal expansion coefficients of the layers in contact. When these stresses become very large [1], they can result in mechanical failure. Choi and Nix studied the internal friction of Cu films from room temperature to 750 K, they indicated the internal friction of thin films at the micrometer scale or nanometer scale could make it possible to identify the relaxation processes associated with grain boundary diffusion and sliding [2]. In previous study of the relaxation of thin Al films on a Si substrate, in which the grain size was shown to be well controlled, varying only with film thickness [3]. In their research, the thicknesses of the films were between 4.6 and 0.6 μm, indicating that the internal friction was associated with grain boundary sliding. Another study compared internal friction between free-standing films and those attached to a substrate [4]. Their research concluded that internal friction in free-standing films is greater than that of film attached to a substrate because the substrate restricts grain boundary sliding near the interface. Y.-T. Wang • Y.-F. Shieh • C.-h. Chen • C.-h. Lu • M.-T. Lin (*) Graduate Institute of Precision Engineering, National Chung Hsing University, 250, Kuo-Kuang Rd., Taichung, Taiwan 40227, Republic of China e-mail: mingtlin@nchu.edu.tw Y.-C. Cheng Graduate Institute of Precision Engineering, National Chung Hsing University, 250, Kuo-Kuang Rd., Taichung, Taiwan 40227, Republic of China Center for Measurement Standards, Industrial Technology Research Institute, Hsinchu, Taiwan 300, Republic of China C.-L.Wu Center for Measurement Standards, Industrial Technology Research Institute, Hsinchu, Taiwan 300, Republic of China B.C. Prorok et al. (eds.), MEMS and Nanotechnology, Volume 8: Proceedings of the 2014 Annual Conference on Experimental and Applied Mechanics, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-07004-9_8, #The Society for Experimental Mechanics, Inc. 2015 67
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