VLSI Gate Dielectric TA ₂ O ₅ Study On Preparation And Characteristics Of Thin Films

With the fast development of VLSI (Very Large Scale Integration), high dielectric constant (high-k) materials have been drawing much attention for replacing conventional gate dielectric material-SiO₂, which is reaching its physical limit. Tantalum pentoxide (Ta₂O₅) is a possible candidate because of its relatively high dielectric constant, low leakage current, high breakdown strength and process compatible.In this dissertation, Ta₂O₅ thin film was deposited by DC reactive magnet sputtering and annealed by RTA (Rapid Thermal Annealing). AFM (Atomic Force Microscope), XRD (X-ray Diffractometer), UVS (Ultraviolet and Visible Spectrophotometer), DST (Dielectric Strength Tester) were performed to investigate the phase composition, surface property, electrical and optical properties of Ta₂O₅ thin film.Research showed that the relationship between ignition voltage and sputtering pressure was according Paschen's Low. Deposition rate was decreased exponentially as increasing of oxygen flow ratio, and first increased then decreased as increasing of sputtering pressure, reached max at 0.3Pa. Surface of the Ta₂O₅ thin films was flat, compact and without any visible defect. Rq (Root-Mean-Sq) of as-deposied Ta₂O₅ thin film ranged from 0.488-2.579nm, which was related with deposition rate. Surface of film was improved when the annealing temperature below crystalline temperature of Ta₂O₅. As-deposited Ta₂O₅ thin film was amorphouse, a hexagonal structure (δ-Ta₂O₅) was identified after annealed at 800℃, another transition fromδ-Ta₂O₅ to low temperature orthorhombic structure (L-Ta₂O₅) occurred at 9001000℃.Ta₂O₅ thin film with a high transmission in visible spectrum was obtained. Index of refraction n was between 2.01-2.20, the order of magnitude of extinction coefficient k was 10^-4, optical band gap and break strength ranged from 3.6-4.3eV and 2-4.5 MV/cm respectively. Dielectric constant of Ta₂O₅ thin film was increased from 24.3-26.5 after annealed at 800℃, then decreased at higher annealing temperature. The results showed that Ta₂O₅ thin film prepared by DC reactive magnet sputtering had good electrical and optical properties.