CONDENSED MATTER DIELECTRIC CHARACTERISTICS AND RELIABILITY TESTS FOR THIN Au-Ta 2 O 5 -SiO 2 -Si STRUCTURES  M. PECOVSKA-GJORGJEVICH 1 , D. SPASOV 2 , N. NOVKOVSKI 1 , E. ATANASSOVA 2 1 Institute of Physics, Faculty of Natural Sciences and Mathematics, St. Cyril and Methodius University, P.O. Box 162 1000 Skopje, Macedonia, pecovska@iunona,pmf,ukim.edu.mk 2 Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee 1784 Sofia, Bulgaria Received December 21, 2004 Au-Ta 2 O 5 -SiO 2 -Si capacitors were studied in order to investigate their dielectric characteristics and reliability. Tantalum pentoxide thin films on Si were prepared by two methods (RF sputtering of Ta in Ar + O 2 and thermal oxidation of tantalum layer on Si, with two thicknesses 50 nm and 17 nm). Films were subjected to post deposition oxygen annealing at 900° C for 30 min. The leakage current density for d = 50 nm is under 10 –7 A/cm 2 at 0.95–1 MV/cm for accumulation and at 0.5–0.64 MV/cm for inversion. For thinner structures (d = 17 nm) leakage current is much higher. Investigation of the conduction mechanism confirms that SE dominates for low fields (till 4 V) and goes to Pool-Frenkel for medium fields (over 4 V) for accumulation regime and for reversed bias fast increase of the current is observed at 3–5 V which may be due to the breakdown of the ultrathin SiO 2 at the interface with Si. For this region the conduction mechanism may be combination of Fowler- Nordheim tunneling (FN) through SiO 2 and PF through Ta 2 O 5 . Reliability tests show different dependences at the first stage for the structures with different thickness and different method of obtaining. Similar curves are observed for all currents injected. Breakdown field is over 2 MV/cm for thicker and ~ 6 MV/cm for thinner films. The structures show good characteristics for DRAM application, although high C-V and quasistatic C-V measurements show high degree of defects in the insulator layers. Key words: Tantalum pentoxide, gold electrode, reliability, DRAM application. 1. INTRODUCTION There is an extended demand for replacing poly silicon gates and silicon oxide with metal gates and alternative high-k gate dielectrics in MOS capacitors because of their thickness limitation. Scaling down the thickness of the film  Paper presented at the 5th International Balkan Workshop on Applied Physics, 5–7 July 2004, Constanþa, Romania. Rom. Journ. Phys., Vol. 50, Nos. 9– 1 0 , P. 1009–1017, Bucharest, 2005