ULTRATHIN TANTALUM OXIDE CAPACITOR PROCESS USING OXYGEN-PLASMA ANNEALING

A highly reliable ultrathin tantalum oxide capacitor is fabricated by using oxygen-plasma annealing after the film deposition. A tantalum ox ide film is deposited on a nitrided polycrystalline silicon surface us ing a mixture of penta-ethoxy-tantalum [Ta(OC2H5)5] and oxygen gas. Th e films are annealed in an oxygen-plasma at less than 400-degrees-C. T he oxygen-plasma annealing greatly reduces the leakage current through tantalum oxide capacitors and produces better time-dependent dielectr ic breakdown characteristics than either dry O2 annealing or two-step annealing (oxygen-plasma + dry O2 annealings). The reason for the exce llent electrical properties is examined using secondary ion mass spect rometry, extended x-ray absorption fine structure spectroscopy, and tr ansmission electron diffraction patterns. Analytical results show that the oxygen-plasma annealed tantalum oxide films are densified by the elimination of carbon and hydrogen and by the repair by oxygen of vaca nt sites in the as-deposited films, as the films remain amorphous duri ng oxygen-plasma annealing. In addition, oxygen-plasma annealing suppr esses thickening of the interface layer between the tantalum oxide fil m and polycrystalline silicon bottom electrode. Therefore, highly reli able ultrathin tantalum oxide capacitors with an SiO2 equivalent thick ness of less than 3 nm can be fabricated by using oxygen-plasma anneal ing.