Ultrasonic Spray Pyrolysis Deposition and Characterization of Tantalum–Aluminum Oxide Thin Films

Abstract

Tantalum oxide and tantalum-aluminum oxide films have been prepared by pyrosol using alcoholic start solution of tantalum chloride and aluminum acetylacetonate at substrates temperatures of 250°C. All films are amorphous independent of the deposition conditions. X-ray diffraction shows that aluminum incorporation in deposited materials stabilizes the amorphous phase even after annealing at 525°C and 900°C. Energy dispersive spectroscopy, Rutherford backscattering, refractive index, and FTIR results indicate that the relative chemical composition of the deposited films is about ͓Ta͔ = 20 atom % and ͓O͔ = 80 atom %, probably containing hydroxide or oxohydroxide groups. The concentration of aluminum in films depends on the concentration of aluminum acetylacetonate in start solution with a ratio ͓Al atom % in film͔/͓Al atom % in solution͔ Ϸ0.1. The rms roughness has values of Ͻ1 nm. The effect of incorporation of aluminum in deposited material and its annealing at 525°C on the electrical characteristics of metal-oxide-metal structures increases the breakdown electric field and decreases the current density. The dielectric constant decreases as the aluminum concentration increases and annealing has a densification effect on the TAO films.Tantalum oxide ͑Ta 2 O 5 ͒ has some physical properties that make it an attractive material from different points of view. Because of its relatively high refractive index and wide bandgap ͑4.4 eV͒, it can be used as optical coating, particularly as an antireflecting coating for solar cells and in optical wave guides. 1 Its electrical conductivity is very sensitive to gaseous elements, such as oxygen, nitrogen, and hydrogen. 2,3 Other important applications of tantalum oxide are as a high-temperature resistance material. 4 From an electrical point of view, given the scaling down of integrated circuits trend the use of silicon dioxide ͑SiO 2 ͒ films as the gate dielectric layer with a thickness of 1.5 nm permits large leakage currents, which results in integrated circuits that do not function properly. It is accepted that if a film of a high dielectric constant ͑high-k͒ material is used to replace SiO 2 , the film thickness can be increased, which drastically reduces the leakage current. 5 Because of its high dielectric constant and good dielectric breakdown strength, Ta 2 O 5 thin film is considered a promising candidate for applications in electronic devices, e.g., electroluminescent devices of the metal/insulator/semiconductor/ insulator/metal ͑MISIM͒ type, dynamic random access memories ͑DRAM͒, decoupling capacitors, and as the gate dielectric layer in metal-oxide-semiconductor ͑MOS͒ devices. 6,7 In general, all these devices must have the lowest leakage electrical current; to accomplish this condition, the dielectric layers must be of amorphous nature to avoid the relatively large currents through the grain boundaries measured in crystalline materials. Nevertheless, the tantalum oxide crystallize at a temperature of the order of 600°C, which is a temperature lower than those used i...

AlxTayOz Mixture Coatings Prepared Using Atomic Layer Deposition for Corrosion Protection of Steel

“…Al x Ta y O z mixture thin films have previously been grown by several methods including sol‐gel,35 spray pyrolysis,36 radiofrequency (RF) sputtering,37, 38 and CVD 39, 40. The dielectric properties achieved with the Al x Ta y O z mixtures were between those of Al 2 O 3 and Ta 2 O 5 35–39. In addition, Hara et al40 showed that Al x Ta y O z mixture films prepared by CVD onto Pt and Si are highly stable in strong acid and alkali solutions.…”