A Trial for Micro-Scale Evaluation of Adhesion Strength around Cu Metallization Systems
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A Trial for Micro-Scale Evaluation of Adhesion Strength around Cu Metallization Systems Shoji Kamiya1, Hitoshi Arakawa1, Hiroshi Shimomura1, and Masaki Omiya2 1 Department of Mechanical Engineering, Nagoya Institute of Technology, Gokiso-cho, Showaku, Nagoya, 446-8555, Japan 2 Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan ABSTRACT Adhesion strength of the interface between Cu film and SiCN cap layer for IC metallization system was evaluated by a technique developed by the authors. In this technique, microscopic specimens with the in-plane dimension less than 10 µm were fabricated by focused ion beam system and loaded directly by a sharp diamond stylus with submicron tip radius. By comparing the crack extension behavior with the three-dimensional numerical simulation, the interface adhesion energy was evaluated to be 5 J/m2. The same interface was subjected also to the four-point bending experiment, which is widely applied to interface adhesion measurement. The evaluation results by the two techniques agreed reasonably well with each other. INTRODUCTION With further increase in the structural density of integrated circuits, adhesion of interface in multi-layered metallization systems has become a serious concern from the viewpoint of mechanical reliability. The four-point bending method developed by Charalambides et al.[1] is now widely accepted in the microelectronics industry as the de-facto standard to evaluate the interface adhesion energy between thin films. Many aspects of interface strength around the new generation of IC metallization systems with Cu and low-k materials were quantitatively surveyed by the four-point bending technique during the past ten years in order to enhance mechanical reliability[2-4] of the systems. However, all of them measured the adhesion with blanket films deposited over the entire wafer and no report was found about the possible local variation of strength. Although it is important to ensure the homogeneity of adhesion or even to evaluate the adhesion of patterned films, it is difficult to locally evaluate the adhesion by applying the four-point bending technique because of the macroscopic scale of the specimens. One of the authors recently established a new scheme of interface strength evaluation. The technique was first developed for wear-resistant hard coatings[5,6], and later applicability to Cu metallization systems was also demonstrated[7]. In this technique, micron-scale specimens are fabricated and loaded directly by a sharp diamond stylus. The adhesion is evaluated in terms of energy release rate by comparing the interface crack extension behavior with the results of numerical simulation. Because of the small specimen size, the technique has a potential to evaluate possible local variation of adhesion and even the adhesion of patterned structure. The study here was concentrated on the evaluation of interface adhesion energy between Cu and a SiCN cap layer for a metallization system by applying our t
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