The brightening additive level and dc current density of electroplating baths are two parameters that affect the gap-filling capability and the degree of impurity incorporation in electroplated copper films. Additive incorporation can inhibit grain growth during the room temperature recrystallization process and therefore affect the final grain size. This investigation explores the grain size and microstructure of dc jet-electroplated copper films in 0.35 and 0.50μm Damascene trenches as a function of current density and brightening additive level after first receiving a high-temperature anneal. Unlike a previous study that explored these variables in blanket Cu films [ J. Electrochem. Soc. , 152 , C101 (2005) ], the results of this study suggest that current density, and to a lesser extent additive level, play a role in determining the final grain size in Damascene trenches. In 0.5μm trench structures it was found that only higher dc current density levels produce larger cross-sectional grain sizes. In 0.35μm trenches, however, both the current density and brightening additive level affected the final grain size. It thus appears that the level of geometrical constraint, the number of available nucleation sites, the amount of stored energy in the microstructure, and the degree of remnant additive incorporation are factors that could influence the final grain size.
Andrew Tzanavaras, Gregory Young, and Stacy H. Gleixner. "The Microstructure and Grain Size of Jet Electroplated Copper Films in Damascene Trench Features" Journal of the Electrochemical Society (2006): c509-c516. doi:10.1149/1.2200287