Material and electrical characterization of carbon-doped Ta_(2)O_(5) films for embedded dynamic random access memory applications

摘要

This work is a systematic study of carbon incorporation in Ta_(2)O_(5) and its effect on the material and electrical properties of Ta_(2)O_(5), a promising replacement for silicon oxide in embedded dynamic random access memory applications. Using pulsed-dc reactive and rf-magnetron sputtering of Ta_(2)O_(5) performed in an argon/oxygen/carbon-dioxide plasma, we have methodically doped the Ta_(2)O_(5) films with carbon. In thick (70 nm) Ta_(2)O_(5) 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 Ta_(2)O_(5) film grown in similar conditions without CO_(2) 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) Ta_(2)O_(5) 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.