High resolution analysis of Cu thin oxide formed on Cu in 32-nm node Cu/low-k application

Three different types of Cu thin oxide layers such as native grown oxide, thermally grown oxide, and plasma-assisted oxide formed on physical vapor deposited Cu (sputter-Cu), provided in the Cu/low-k interconnects for advanced microprocessor units (MPUs), are evaluated with the highest brilliance synchrotron radiation X-ray (SPring-8) and TEM observations. Physical thickness of prepared Cu oxide is ranged from 10-nm to 2-nm. For plasma-assisted Cu oxide, there is weak Cu₂O and/or CuO X-ray diffraction pattern while no diffraction pattern in native and thermally (170degC) grown oxides. However, native and thermal oxides have Cu₂O coordination observed by XANES (X-ray absorption near edge structure) method. This suggests that Cu oxide formed at low temperatures consists of stoichiometric Cu₂O in an amorphous structure. Thickness estimated by the GIXR (grazing incidence X-ray reflectively) measurement is 50% to 80% thinner than that of physical thickness. The activation energy of Cu oxidation is obtained at 0.76 eV