Charge trapping during constant current stress in Hf-doped Ta2O5 films sputtered on nitrided Si

• Published in: Thin solid films Vol. 519; no. 7; pp. 2262 - 2267
• Main Authors: NOVKOVSKI, N, ATANASSOVA, E
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier 31.01.2011
• Subjects: Charge; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Deposition by sputtering; Dielectric thin films; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Electron and ion emission by liquids and solids; impact phenomena; Exact sciences and technology; Field emission, ionization, evaporation, and desorption; Hafnium; Leakage current; Materials science; Mechanical and acoustical properties; Methods of deposition of films and coatings; film growth and epitaxy; Physical properties of thin films, nonelectronic; Physics; Silicon; Stresses; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Tantalum oxides; Thin films; Trapping; Vacancies; Tantalum oxide; Active site; Doping; Mechanical properties; Oxides; Field emission; Dielectrics; Leakage currents; Thin films; Interfaces; Kinetic model; Trapping; Tantalum; Wear; Dielectric thin films; Hafnium; High field; Stress effects; Silicon; Sputter deposition; Reliability; Current density; Tribology
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2010.10.063

Metal-insulator-silicon structures containing Hf-doped Ta2O5 dielectric films sputtered on rapid thermally nitrided Si are shown to have very good reliability properties. Stress-induced leakage currents are low, both at low and at high-fields. It is found that charge trapping during the stress is the dominant wear-out mode for very long stress times of 500s even for injected current densities J s as high as 100mA/cm2. Stress curves approach saturation at long stress time, indicating that the trap generation rate is very low, even compared to the observed reduced trapping at pre-existing traps. Applying a trapping kinetics model, two trapping sites with characteristic trapping times tau 1 =3.2s and tau 2 =49s were determined and attributed to pre-existing defects in the bulk Hf:Ta2O5 layer and not in the interfacial SiOxNy layer. It was found that both tau 1 and tau 2 do not depend on J s, which may be explained by the presence of a mechanism of charging the active sites through field activated emission of charge from them.