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B5.2.1

Structure Evolution in Plated Cu Films D.P. Field1, NJ Park1,2, PR Besser3, and JE Sanchez Jr.4 School of Mech. and Matls. Eng, Washington State University, Pullman, WA 99164-2920 USA 2 Kumoh National Institute of Technology, Gumi, Gyungbuk, 730-701 Korea 3 Advanced Micro Devices, Sunnyvale, CA 94088-3453 USA 4 Unity Semiconductor, Sunnyvale, CA 94085 USA 1

ABSTRACT Structure evolution in plated Cu films is a function of sublayer stacking, film thickness, plating chemistry, plating parameters, and temperature. The present work examines grain growth and texture evolution in annealed plated Cu on a 25 nm thick Ta sublayer for films of 480 and 750 nm in thickness. These results are compared against those obtained from damascene Cu lines fabricated from a similar process, using a series of line widths. The results show that the initial structures of the plated films are similar, with slightly weaker (111) texture, a higher fraction of twin boundaries, and larger grains in the thicker films. The microstructure of the Cu within the trench constraints is a strong function of line geometry with the propensity for twin boundary development controlling structural evolution.

INTRODUCTION The fabrication of integrated circuits involves thermal cycling through various processes of metal and dielectric deposition. This results in the potential for considerable structural evolution in the conducting films and lines subsequent to the initial deposition. The difference in the thermal expansion coefficients of the metal and the substrate and surrounding materials develops high stresses in the films and interconnect lines that contribute to the observed behavior. Copper provides many advantages over the previous Al interconnect strategy, but film and line fabrication still needs to improve in terms of manufacturability and reliability. During thermal processing, annealing twins including {511}, {522}, {211}, and {322} textures [1], can form in the Cu films. As the twins develop, the texture strength necessarily weakens since these new orientations develop. Grain size and crystallographic texture influence structural stability during thermal cycling, and play an important role in controlling processes such as stress voiding and electromigration [2-8]. Therefore, understanding microstructural evolution in these materials is important in developing fabrication procedures for these structures so processes can be identified that optimize structural stability and uniformity. Grain growth and texture evolution during fabrication of Cu films is complex and depends on many different factors, such as the film thickness, the substrate material and stress state, film deposition parameters, plating bath chemistry, annealing temperature and time, alloying and geometrical constraints [9-13]. In this study the problem has been constrained to investigate grain growth and texture formation as a function of film thickness and heat-treatment. The sublayer material, alloy and plating conditions are similar for all films and line structures inves