Atomic force microscopy and Raman spectroscopy studies on the oxidation of Cu thin films

The oxidation of sputtering deposited copper thin films has been investigated. Phase identification and surface morphology characterization were performed by x-ray diffraction, Raman spectroscopy, and atomic force microscopy (AFM). The copper film is first oxidized to Cu2O below 300 °C and then to CuO at higher temperatures (≥300 °C) near the surface of the copper. AFM results show that the as-deposited Cu film contains grains of similar sizes. After heat treatment at 200 °C, small grains are observed due to nucleation of the Cu2O phase. Further annealing in air leads to aggregation and growth of the grains whereas the grain boundary of the grains before coalescence is still evident. The Cu2O and CuO phases form alternating layers when the annealing temperature is 400 °C.