Effect of Cu contamination on recombination of O atoms on a plasma-oxidized silicon surface

In the dual damascene microelectronics integration scheme during the last stage of plasma etching of dielectrics down to underlying Cu layers, Cu is sputtered onto the reactor walls and is believed to cause a drift in etching rates. For photoresist etching in an O(2)-containing plasma, a drop in etching rate suggests that Cu could cause a decrease in the O-atom concentration in the plasma, due perhaps to an increase in the O recombination rate on the chamber walls. We therefore studied the effects of traces of Cu on O recombination on an oxygen plasma-conditioned surface, using the spinning wall technique. With this method, a cylindrical substrate, here coated in situ with sputter-deposited Si and then oxidized in an O(2) plasma, is rotated past skimmers, allowing the surface to be periodically exposed to the plasma and an Auger electron spectrometer with a pressure gauge in a differentially pumped chamber. Between plasma exposures, the sample could also be dosed with Cu from an evaporation source in a differentially pumped chamber. With no Cu on the surface, a pressure rise was observed in the Auger chamber, due to desorption of recombined O(2). These measurements were used to derive a Langmuir-Hinshelwood recombination coefficient of gamma(O)=0.043 for the steady-state oxidized Si, Cu-free surface. The surface was then coated with a small fraction of a monolayer (roughly similar to 0.002 monolayers of Cu with a dose of similar to 1.4 X 10(13) cm(-2) and an assumed sticking coefficient of 0.3) and gamma(O) was found to increase to 0.069. Further dosing with Cu did not produce any further increases in gamma(O). The initial low gamma O value could not be recovered by coating the surface with sputter Si, apparently due to rapid outdiffusion of Cu through Si at room temperature. Cu catalyzed recombination of O is ascribed to a redox cycling between Cu(+) and Cu(2+) oxidation states. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3143107]