Dynamic Stress Analysis Applied to the Electrodeposition of Copper
Manon C. Lafouresse, Ugo Bertocci, Gery R. Stafford
Stress development during the electrodeposition of copper from additive-free, acidic CuSO_(4) electrolyte was analyzed by dynamic stress analysis, an in situ characterization technique that combines electrochemical impedance spectroscopy with cantilever curvature. Two sources of stress account for the dynamic stress behavior in the frequency range of 0.1 Hz to 25 Hz. The high frequency region is controlled by electrocapillarity (charge-induced stress). The stress is 180° out of phase with the input potential, and its amplitude is relatively small. Low frequency is dominated by the growth stress of the Cu film, which under the conditions examined here is tensile. The amplitude of the stress response increases with decreasing frequency and its phase angle shifts from +180° to +90°. Both of these transitions are potential dependent and can be simulated from the electrochemical impedance, making use of separate stress-charge coefficients for double layer charging and Cu deposition. Since these stress-generating mechanisms have dramatically different frequency dependence, Cu deposition is a nice demonstration that highlights the attributes of DSA; i.e., using frequency to separate the various stress contributions.