Tantalum oxides have been prepared by thermal oxidation of sputtered tantalum fils and LPCVD on silicon and silicon dioxide substrates at temperature between 450$^\circ$C and 700$^\circ$C. The composition of such oxide is tantalum pentoxide ($Ta_2O_5$) and amount of silicon diffused into the tantalum oxide from the Si substrate increases as the oxidation temperature increases. The degree of short range order of the amorphous tantalum oxide changes with the oxidation temperature. The temperature dependence of the dielectric constant of $Ta_2O_5$ on Si can be explained in terms of its silicon concentration and short range order of noncrystalline. C-V curves of Al/$Ta_2O_5$/Si capacitors show the presence of donor type interface states whose density decreases as the oxidation temperature increases. The flat band voltage of Al/$Ta_2O_5$/Si capacitors become more negative as the oxidation or annealing temperature increases regardless of the annealing ambient.
The formation of $SiO_2$ layer at $Ta_2O_5$/Si interface is observed by annealing in dry $O_2$ or $N_2$ and the thickness of this layer increases with the annealing temperature. Leakage current of thin(less than 40nm thick) $Ta_2O_5$ films decreases as a annealing temperature increases in dry $O_2$ or $N_2$. The dielectric constant vs. annealing temperature curve shows a maximum peak at 750$^\circ$C or 800$^\circ$C resulting from the crystallization. It becomes domianant for thicker $Ta_2O_5$ films. But it decreases at higher annealing temperature due to the growth of interface $SiO_2$. The flat band voltage and gate voltage instability as a function of annealing temperature can be explained in terms of the growth of interface $SiO_2$. The electrical properties of $Ta_2O_5$ as a function of annealing conditions do not depend on the fabrication method of $Ta_2O_5$ but strongly depend on the thickness of $Ta_2O_5$.
