Metal gates and gate-deposition-induced defects in Ta2O5 stack capacitors

The effect of various electrodes (Al, W, TiN) deposited by evaporation (Al) and sputtering (W, TiN) on the electrical characteristics of Ta2O5 stack capacitors has been investigated. The leakage currents, breakdown fields, mechanism of conductivity and dielectric constant are discussed in the terms of possible reactions between Ta2O5 and electrode material as well as electrode-deposition-process-induced defects acting as electrically active centers. During deposition of TiN and Al a reaction that worsens the properties of Ta2O5 occurs while there is not an indication for detectable reduction of Ta2O5 when top electrode is W. The sputtered W top electrode is a good candidate as a gate of storage capacitors in DRAMs, but sputtering technique is less suitable for deposition of TiN due to the introduction of radiation defects causing deterioration of leakage current. Although some reaction between Al and Ta2O5 occurs, the resulting electrical properties of the capacitors are still acceptable.