Magnetron‐sputtered Ta2O5 films on Si are analyzed for their applications to semiconductor devices. It is clarified that the transition region formed at the Ta2O5/Si interface plays a significant role in determining electrical characteristics. This transition region formed during the initial stage of deposition consists of a mixture of Ta, Si, and O, and its thickness is in the range of 4 to 6 nm. The composition profile of this transition region and its thickness depend on two dominant factors: (1) oxygen partial pressure in the sputtering gas and (2) the surface oxide thickness on Si prior to deposition. Furthermore, it is initially indicated that 2.5‐nm‐thick surface oxide formed on Si prior to deposition produces a significant deterioration in leakage current. By reducing the surface oxide thickness to as low as 1.8 nm and adjusting the oxygen partial pressure, an optimum transition region is formed, which makes it possible to obtain high‐quality Ta2O5 films with high dielectric breakdown strength exceeding 6 MV/cm and low leakage current of <109 A/cm2 (at 1 MV/cm).

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