A Study On The Preparation Of Tantalum Oxide Films By Mid-Frequency AC Reactive Sputtering And Their Dielectric Properties

Dielectric thin film was an important kind of electronic thin films, which has wide applications in microelectronic and photo-electronic technology. With the demands of large integration of capacitors, Silicon Oxide (SiO2) has approached its thickness limitation. Tantalum Oxide (Ta2O5) attracts more attentions because of its high dielectric constant, stable thermal and chemical properties. It might become the most promising candidate high constant dielectric thin films applied in industries. The dissertations focus on the preparation, electrical properties of Ta2O5 and how to improve its insulation properties. Tantalum oxide films were prepared by self-assembled middle frequency a.c. sputtering system. The contents and microstructure of the films were studies as the functions of oxygen percentage in sputtering gases and substrate temperature. The stoichiometric films were prepared by optimizing processing parameters. The deposition characteristics were studied. The effects and mechanisms of oxygen percentage and thickness on the refractive constant were analyzed. The work mainly focuses on the study of electrical properties of Ta2O5. The conduction and breakdown mechanism of the films were tested and studied. The results showed that with the increase of the field strength, the conduction of the films was separately dominated by Ohm's Law, Schottcky Effect, Pool-Frenkel Effect, and Fowler-Nordheim tunneling breakdown. The electrical properties as the function of oxygen percentage, defects in the films, and the roughness of the substrate surface were investigated. The dielectric of the films was 20~30 (10~20kHz), the dielectric loss tangent was 0.001(20kHz). The best result was obtained: the breakdown field was 2.22MV/cm, and the leakage current density was lower than 1×10-8A/cm2 with the top electrode of1.0mm in diameter; The highest breakdown field was 4.0MV/cm with 0.5mm in diameter, which was higher than 3.8MV/cm reported in other references by the same method.The MIM structure of high quality was fabricated by reducing the area of top-electrode and pretreatment on substrates, and the yield was also improved by these two methods. The electrical properties become worse and yield degraded with the larger top-electrode area and rougher substrate.The as-deposited tantalum oxide films were post-processed by anodic oxidation. The micropores in the films were filled and Ta atoms were fully oxidized compared to as-deposited films. In addition, these films exhibit greatly improved leakage currents and breakdown field strength.