Conduction mechanisms and reliability of thermal Ta2O5–Si structures and the effect of the gate electrode

• Published in: Journal of applied physics Vol. 97; no. 9
• Main Authors: Atanassova, E., Paskaleva, A., Novkovski, N., Georgieva, M.
• Format: Journal Article
• Language: English
• Published: 01.05.2005
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.1884758

The effect of metal gate electrodes (Al, W, Au, TiN, and TiN∕W) on dielectric properties, leakage currents, conduction mechanisms, and reliability characteristics of metal-oxide-semiconductor capacitors with thermal Ta2O5 is investigated. The results are discussed in terms of the relative influence of the gate deposition techniques and the intrinsic properties of the electrode material and the former appears to be more pronounced. It is found that some parameters such as interface state density, breakdown fields, and charge trapping are defined mainly by the properties of Ta2O5 itself. The global dielectric constant of the stack dielectric, oxide charge, leakage current level at high applied fields, charge-to-breakdown, and stress-induced leakage currents are remarkably affected by the upper electrode. It is concluded that the nature and spatial distribution of the gate deposition-induced defects are sensitive to the technological process (evaporation or sputtering); this effect is so strong that it tends to outweigh the effect of the intrinsic properties (e.g., work function) of the gate material. The bulk-limited Poole–Frenkel emission is the dominant conduction mechanism in Ta2O5. A Au gate is preferable and shows the best parameters in terms of the leakage current and stress-induced leakage current, whereas Al-gate capacitors reveal the best dielectric constant and charge to breakdown.