Characterization of Cu surface cleaning by hydrogen plasma

When a Cu surface is exposed to a clean room ambient, a surface layer conta ining Cu2O, CUO, Cu(OH)(2), and CuCO3 is formed. Thermal treatment in a vac uum combined with hydrogen plasma can remove this layer. Water and carbon d ioxide desorb during the thermal treatment and the hydrogen plasma reduces the remaining Cu oxide. Ellipsometric, x-ray photoelectron spectroscopy, an d time-of-flight secondary ion mass spectroscopy analyses indicate that the mechanism of interaction of the H-2 plasma with this layer depends on temp erature. When the temperature is below 150 degreesC, H-2 plasma cannot comp letely reduce Cu oxide. Hydrogen diffuses through the oxide and hydrogenati on of the Cu laver is observed. The hydrogenated Cu surface has a higher re sistance than a nontreated Cu layer. The hydrogen plasma efficiently cleans the Cu surface when the substrate temperature is higher than 150 degreesC. In this case, hydrogen atoms have enough activation energy to reduce Cu ox ide and adsorbed water forms as a byproduct of Cu oxide reduction. When the wafer temperature is higher than 350 degreesC, the interaction of the Cu f ilm with hydrogen and residual oxygen is observed. (C) 2001 American Vacuum Society.