1e:T4c9,The chemical structure and dielectric characteristics are investigated for amorphous tantalum pentoxide films 6–40 nm thick deposited on Si by reactive sputtering. An x‐ray photospectroscopy study shows that a thin layer grows at the interface during the deposition. Clear boundaries between the , , and silicon substrate are observed using a cross‐sectional transmission electron microscope picture. The measured dielectric constant decreases as the film thickness decreases. This is explained by assuming that the thickness at the interface is 2.4 nm. The product of this dielectric constant and the electric field at a leakage current of 10−2 A/cm2 for the double layers decreases. It goes from 104 to 36 MV/cm as the film thickness decreases over a thickness range of about 10–40 nm. However, it remains constant about 10 nm and below. These phenomena are explained by assuming that the leakage current through the film is limited by bulk limited conduction for films whose thickness exceeds 10 nm. On the other hand, in films less than 10 nm thick, either direct tunneling or Fowler‐Nordheim conduction begins. This conduction is limited by electron injection into the at the interface from the Si substrate.1f:T455,Tantalum pentoxide is of interest as an alternative dielectric to SiO 2 for MOS devices. In the present work, RF-sputtered tantalum films on silicon substrates were thermally oxidized at 500°C. Ellipso-metric measurements showed that films made in this way were uniform in refractive index except for a narrow region of tapered index at the silicon interface. Capacitance measurements gave a relative permittivity of about 26, in the range shown by anodic Ta 2 O 5 films. The conduction currents depended on the oxidation period but were comparable to or slightly better than reported for CVD Ta 2 O 5 .

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