Effect of plating current density and annealing on impurities in electroplated Cu film

This study uses secondary-ion-mass spectrometry to examine the effects of plating current density and annealing temperature on the nature of electroplated copper (Cu) films. The experimental results reveal that high levels of impurities, such as C, O, S, and Cl, are incorporated into Cu deposits at the lower current density region while superfilling occurs. The C and O impurities can be released from the plated films by thermal annealing, while S and Cl cannot. This work proposes a possible mechanism based on bond strength to explain the phenomena. Rapid C and O desorption is observed when the films are first cycled to 220 °C immediately after electroplating. The activation energy of C desorption is found to be approximately 9.8 kJmol. For Cu electroplating, this investigation suggests that high plating current density and an adequate annealing temperature are required to reduce impurities.