Material and electrical characterization of carbon-doped Ta2O5 films for embedded dynamic random access memory applications

This work is a systematic study of carbon incorporation in Ta2O5 and its effect on the material and electrical properties of Ta2O5, a promising replacement for silicon oxide in embedded dynamic random access memory applications. Using pulsed-dc reactive and rf-magnetron sputtering of Ta2O5 performed in an argon/oxygen/carbon-dioxide plasma, we have methodically doped the Ta2O5 films with carbon. In thick (70 nm) Ta2O5 films, an optimal amount (0.8-1.4 at. %) of carbon doping reduced the leakage current to 10(-8) A/cm(2) at +3 MV/cm, a four orders of magnitude reduction compared to a leakage current of 10(-4) A/cm(2) in an undoped Ta2O5 film grown in similar conditions without CO2 in the plasma. This finding suggests that carbon doping can further improve the dielectric leakage property at an optimal concentration. X-ray Photoemission Spectroscopy analysis showed the presence of carbonate (carbon bonded to three oxygen) in these electrically improved carbon-doped films. Analysis by high-resolution transmission electron microscopy and Nomarsky microscopy exhibited no morphological or structural changes in these carbon-doped thin films. Moreover, carbon doping showed no improvement in the leakage current in thin (10 nm) Ta2O5 films. This phenomenon is explained by a defect compensation mechanism in which the carbon-related defects remove carriers at low concentrations but form a hopping conduction path at high concentrations. (C) 2002 American Institute of Physics.