In this paper, we have studied the segregation phenomenon of Cu on the surfaces of patterned lines, dry-etched films and non-etched films, by using X-ray photoelectron spectroscopy and lower energy Rutherford Backscattering Spectrometry. Significant enrichment of Cu is found on the sidewall of the lines. Annealing at 350°C and above cause the disappearance of this enrichment. Origin and evolution of this Cu enrichment have been investigated on films taken out from different steps of the etching process. It has been found that most of the Cu products induced by the plasma etching are CuCl and CuCl2 and they are removed mostly from the top Al oxide layer by the strip process. On the interface area between Al and the native oxide, considerable quantities of etched induced Cu are retained. This Cu is identified to be mainly metallic Cu. Different from the mechanism explained above, thermal annealing can also cause Cu segregation. We have found that Cu atoms diffuse into the native Al oxide where they form Cu2O.