A comparative study of a new microscale technique and conventional bending techniques for evaluating the interface adhes
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Hiroshi Shimomura Nagoya Institute of Technology, Department of Mechanical Engineering, Aichi 466-8555, Nagoya, Japan
Masaki Omiyaa) Keio University, Department of Mechanical Engineering, Kohoku-ku Yokohama, Kanagawa 223-8522, Japan; and JST CREST, Chiyoda-ku, Tokyo 102-0075, Japan
Takashi Suzuki Fujitsu Laboratories Ltd., Kanagawa 243-0197, Japan (Received 6 April 2010; accepted 21 June 2010)
We developed a new microscale technique for evaluating the local interface adhesion in a thin film stack and we compared it with a conventional four-point bending technique. Using the microscale technique, the interface adhesion was estimated to be 3.0 J/m2 by comparing experimental results with numerical simulation results for interface crack propagation behavior. The four-point bending technique was applied to the same interface and the interface adhesion was estimated to be 4.4 J/m2 by experiment. However, this value is an overestimate because it includes the plastic deformation of epoxy resin used to fabricate the specimens. By eliminating the additional energy dissipated through plastic deformation of the epoxy resin close to the interface crack tip, the interface adhesion was evaluated to be 3.3 J/m2. This value agrees well with that obtained using the microscale technique.
I. INTRODUCTION
Integrated circuits (ICs) are used in many electronic devices including personal computers and mobile phones. The recent rapid development of ICs requires thin film interconnections to be further miniaturized to submicron scales for faster operation at frequencies over the gigahertz range. Therefore, many ICs now use multilayered copper (Cu) metallization systems that have lower electrical resistances than aluminum (Al), which was conventionally used as the interconnect material. However, these metallization systems have weak adhesion at the interface between the cap layer or barrier metal and the Cu thin film. Interface adhesion in Cu metallization systems has become a major concern in terms of mechanical reliability. Therefore, it is essential to quantitatively evaluate interface adhesion. Various methods have been proposed for evaluating interface adhesion, including the peel test,1,2 the scratch test,3,4 and the indentation test.5,6 The four-point bending a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0258 J. Mater. Res., Vol. 25, No. 10, Oct 2010
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technique developed by Charalambides et al.7 is the most widely used method in the IC industry and it has become the de facto standard for evaluating interface adhesion. With the goal of enhancing the mechanical reliability of IC metallization systems, many aspects of interface adhesion in these systems have been quantitatively surveyed using the four-point bending technique.8–10 The four-point bending technique is relatively simple, but it suffers from two problems. One problem is that it includes the plastic deformation of epoxy resin (used to attach the specimen to the du
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