Recrystallization effects in Cu electrodeposits used in fine line damascene structures

Resistance transformations in blanket films and damascene Lines of electrop lated Cu were investigated to gain insight regarding the recrystallization kinetics of electrochemically deposited Cu in constrained deep submicron fe atures. The study examined grain transformations in blanket;Cu films with t hicknesses ranging from 0.8 to 3.3 mum and Cu damascene Lines with widths f rom 0.25 pm to approximately 1.0 mum. Bulk film resistivity changes were fo und to be directly related to new grain formation and growth (recrystalliza tion) observed in the films. By monitoring the electrical properties of the continuous and patterned films, it was observed that damascene lines of Cu required longer times to achieve the same degree of bulk resistivity chang e when compared with blanket films. For example, at room temperature, a 0.3 5 mum wider x 0.8 mum high Cu line underwent only half the resistive transf ormation over an 865 h period (36 days) that was completed in 120 h (5 days ) in a 0.8 mum blanket Cu film. Microstructural images of damascene structu res, using a focused ion-beam microscope, clearly indicated that wider Cu l ines transform much faster than narrower ones. To investigate the recrystal lization kinetics, samples, prepared under identical conditions, were annea led at different temperatures and times. The recrystallization activation e nergies derived using an Arrhenius model (under isoresistivity conditions) were found to be approximately 0.8 eV:for all Cu films and Lines regardless of geometry. The study indicates that although the overall rate of recryst allization of Cu was very different and dependant on physical geometrical c onstraints, the grain growth mechanism was the same for all Cu films and li nes. (C) 2001 American Vacuum Society.