In this study, Cu-alloy leadframes with (001) preferred orientation and Cu thin films deposited on TiN/Si substrate by metalorganic chemical vapor deposition have been oxidized in alkaline solution of which pH was 12.95. Transmission electron microscopy has been employed to investigate oxidation behavior : oxide phases, morphologies, oxide structure and orientation relationships between Cu and Cu oxides.
It has been observed that the oxides formed on Cu-alloy leadframe and Cu thin film were both needle-like structure and composed of two phases - CuO and $Cu_2O$.
At initial oxidation stage, not all surfaces of Cu were covered with oxide whiskers, whiskers were formed at only some regions which had defects such as grain boundaries, stacking faults, etc. Several orientation relationships between Cu grains and $Cu_2O$ phases of oxide whiskers were revealed at Cu-alloy leadframe and Cu thin films by selective area electron diffraction. High resolution electron microscope study showed that oxide whisker grew at Cu/oxide interface as a single crystal $Cu_2O$ initially, but very small $Cu_2O$ crystals whose diameters were less than 10nm were discovered at the tip of a whisker.
The length and width of the whiskers increased and curled with increasing oxidation time, but the degree of orientation relation decreased. After 20-minute oxidation, no orientation relationship between Cu and $Cu_2O$ was observed.
