Influences of Hydrogen on the Evolution of the Electrical Resistivity Of Ultra-Thin Sputtered Copper Films Measured in R
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Influences of Hydrogen on the Evolution of the Electrical Resistivity Of Ultra-Thin Sputtered Copper Films Measured in Real-Time E. V. Barnat, P. -I. Wang, D. Nagakura and T. –M. Lu Department of Physics, Applied Physics and Astronomy and The Center for Integrated Electronics and Electronics Manufacturing (CIEEM), Rensselaer Polytechnic Institute, Troy, NY 12180-3590, USA ABSTRACT The electrical resistivities of copper films sputtered in either argon or an argon-hydrogen atmosphere are measured in real time, during growth. The electrical resistivities for both cases are observed to be functions of the film’s thickness, with the films grown in the hydrogen containing atmosphere possessing a resistivity of 4.5 +/- 0.2 µΩ-cm at 40 nm, lower than the resistivity of 5.0 +/-0.3 µΩ-cm for 40 nm thick films grown in the argon atmosphere. Furthermore, the electrical resistivities for both sets of films were observed to continue to evolve after the termination of deposition. The amount of change and the rate of change were observed to depend on the film’s thickness as well as atmosphere the films were grown in. Measurements made by X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that the presence of hydrogen also influences the preferential crystallographic orientation as well as grain size distribution. These measurements indicate that the differences in the microstructure are correlated to the observed differences in the behavior of the electrical resistivities.
INTRODUCTION Copper has become the conductor of choice in ultra large-scale integrated circuits because it offers a lower bulk resistivity of 1.67 µΩ-cm than aluminum’s 2.65 µΩ-cm, allowing for the reduction in the delay of signal propagation caused by the resistive nature of the interconnects and the capacitive coupling between adjacent interconnects. As the conductor approaches the size scales comparable to the mean free path of the conduction electrons, size effects may impose limitations on the ultimate resistivity achievable by the copper interconnects. Several studies [1-3] have been performed to determine what these “size effects” are and how these effects influence the electrical resistivity as a function of thickness. Central to these studies was the discussion of electronic scattering and the relation of the electronic scattering to the physical structure of the film. Because of the dependence of the electrical resistivity on the film’s physical structure, and the dependence of the film’s structure on the technique used to grow the film, we have employed a technique to observe the resistivity of a thin film under various growth conditions. In a previous study, a low concentration of hydrogen in the sputtering atmosphere was observed to influence the post deposition annealing behavior of thin copper films [4]. In this study, we examine the influence the presence of a small amount of hydrogen has on the evolution of the electrical resistivity of sputtered copper films and compare it to the evolution of copper films grown under id
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