Nanoscale investigation of long-term native oxidation of Cu films

The long-term native oxidation of Cu films has been investigated at the nanoscale by angle resolved X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and high-resolution transmission electron microscopy. Cu films with different microstructures and crystallographic textures were deposited by with or without a negative substrate bias voltage of - 50 V. The oxidation rate of the Cu films deposited at - 50 V is much lower than that of the Cu films deposited at 0 V. The electron microscopy observation showed that the Cu films deposited at 0 V have two oxide layers, namely, an outer CuO and an inner Cu₂O, whereas the oxide layer of the Cu films deposited at - 50 V consists of only Cu₂O layer. The difference of texture between the Cu films deposited at 0 V and - 50 V is found to affect native oxidation behavior. It is also considered that many defects in the Cu films deposited at 0 V provide preferential nucleation sites and subsequent growth, which promotes Cu oxidation. The difference in the oxidation behavior of the two Cu films and high-purity bulk Cu can be mainly explained by the difference in texture and microstructure.