Microstructural Analysis of Copper Thin Films for Characterization of Stress-induced Voiding Mechanisms

The amount of twin formation of electroplated and thermally treated copper thin films was evaluated by electron back-scattering diffraction (EBSD) analysis. The result establishes the importance of twin formation in the analysis of stress-induced voiding, and indicates that with the inclusion of a copper alloy co-element, twin formation was significantly reduced relative to pure-copper. Furthermore, the thermal stress hysteresis curve of the Cu-Sn(0.01wt%) thin film indicated a higher flow stress than that of pure-copper. These indications are consistent with the theory of suppressed grain deformation and reduced grain boundary elimination by particle pinning of grain boundaries during microstructure evolution of electroplated copper thin film. With the growth of the grains inhibited, both boundary filling and vacancy generation issues are suppressed, and the number of twin boundaries as void nucleation sites are reduced. Thus, the copper alloy film is believed to be more resistant to stress-induced voiding.