O2 plasma oxidation of sputter-deposited Cu thin film during photo resist ashing

O2 plasma oxidation of sputter-deposited copper thin film during photoresist ashing has been investigated by X-ray diffraction (XRD), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The copper thin film was oxidized by O2 plasma under a typical condition to remove photoresist. O2 pressure was 700 mTorr and 500 W radio frequency power was supplied. Substrate was held at room temperature before plasma generation and it was not heated additionally during plasma treatment. After O2 plasma treatment, a new surface oxide layer was formed on copper film. It was found from electron diffraction and Auger electron depth profiling that the plasma-induced oxide had an oxygen deficient Cu2O1−x structure compared to the conventional thermal oxide. The oxide layer was composed of very small and relatively tightly packed grains typically 25 nm in diameter and with random orientation on large grains of copper. The topography of plasma-induced oxide layer was close to that of thermal oxide formed at a low temperature, but the oxidation rate of plasma oxidation was relatively high and seemed to follow an oxidation law at relatively high temperature.