ELLIPSOMETRIC STUDIES ON THE OXIDATION OF THIN COPPER-FILMS

The oxidation of thin copper films was studied using an automatic spectroscopic ellipsometer (wavelength range 410-920 nm). The copper films 50-70 nm thick deposited onto glass substrates under ultrahigh vacuum conditions were exposed to oxygen at 105-degrees-C at a fixed oxygen pressure of 4 Pa. Emphasis was put on the early stages of oxidation starting with clean metal surfaces. It was found that the optical spectra of the pure copper films and the bulk material correspond rather well. The thickness and effective dielectric functions of the oxide films were determined at various stages of oxidation. Some discrepancies were observed between values published by other researchers, mainly the thickness dependent absorption peak in epsilon2 at about 600 nm. Model calculations show that these discrepancies can be traced back to a rough Cu2O-copper interface,