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22 July 2003 Imaging the microstructure of copper with the atomic force microscope (AFM) and ultrasonic force microscope (UFM)
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The material being used to construct interconnects in microelectronic circuitry is changing as developers switch from aluminum alloys to copper in order to make increasing smaller circuit wires. The performance of copper interconnects can be adversely affected by electromigration, precipitation formation, and changes in the grain microstructure of the wire. There is a need for characterization methods that can allow examination of the interconnects/wires and their grain structure in the nanometer range. One of the most powerful tools that are routinely used for characterization of nanostructured materials is the Atomic Force Microscope. The combination of AFM with ultrasonics (UFM) allows a near field acoustic microscopic image to be generated. By having the AFM tip detect the ultrasonic signal, the lateral resolution limitation of the acoustic wavelength that occurs in conventional acoustic microscopy can be overcome so that imaging with nanometer resolution is possible. In this paper, we present a qualitative comparison of AFM-UFM images on different forms of copper nanograins from two sources namely, ion beam deposited thin films samples containing polycrystalline sections and the aligned copper grains in the wires of an actual working microelectronic device. Images of the nanometer grain structure will be presented. Explanations for the image differences between samples will be discussed and possible applications are suggested.
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Carl J. Druffner, Edward J. Schumaker, Paul T. Murray, and Shamachary Sathish "Imaging the microstructure of copper with the atomic force microscope (AFM) and ultrasonic force microscope (UFM)", Proc. SPIE 5045, Testing, Reliability, and Application of Micro- and Nano-Material Systems, (22 July 2003);

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