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Ta 2 O 5 thin films were fabricated by pulsed plasma-enhanced chemical vapor deposition (PECVD) with simultaneous delivery of O2 and the metal precursor. By appropriately controlling the gas-phase environment self-limiting deposition at controllable rates (∼1Å/pulse) was obtained. The process was insensitive to substrate temperature, with a constant deposition rate observed from 90to350°C. As-deposited Ta2O5 films under these conditions displayed good dielectric properties. Performance improvements correlate strongly with film density and composition as measured by spectroscopic ellipsometry and Fourier transform infrared spectroscopy. Pulsed PECVD eliminates the need for gas actuation and inert purge steps required by atomic layer deposition.

Self-limiting growth of Al 2 O 3 is accomplished using both pulsed plasma-enhanced (PE) CVD and plasma-enhanced atomic layer deposition (PEALD). In pulsed PECVD the two reactants (Al(CH 3 ) 3 /TMA and O 2 ) are supplied continuously, while in PEALD the TMA is delivered in pulses separated by purge steps. For both processes the rate per cycle saturates with $200 L of TMA exposure. At 165 8C a rate of 1.37 Å per cycle is obtained using PEALD. For pulsed PECVD the rate scales linearly with the TMA partial pressure, and its extrapolation is in good agreement with PEALD. The results suggest that deposition in pulsed PECVD involves an ALD component which is supplemented by PECVD growth, and that the contribution of the latter may be tuned using the TMA partial pressure. Experiments using patterned wafers support this hypothesis. Conformal coatings are observed within 10:1 aspect ratio trenches using pulsed PECVD; however the deposition rate on the surface of these substrates is greater than within the trench. The ratio between the two corresponds well to the ratio of rates obtained from pulsed PECVD and PEALD on planar substrates. With cycle times <1 s, net rates up to 20 nm min À1 are obtained by pulsed PECVD while retaining high quality and digital control.

Tantalum oxide films were deposited by pulsed and continuous wave ͑CW͒ plasma-enhanced chemical vapor deposition ͑PECVD͒. The pulsed films were stoichiometric and free of impurities as measured by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. CW films contained significant amounts of hydroxyl impurities, resulting in a nonstoichiometric composition with an O/Ta ratio of ϳ2.8. Impedance spectroscopy was used to quantify ion transport through electrochromic half-cells formed by depositing tantalum oxide on both tungsten and vanadium oxides. Logarithmic plots of the imaginary component of impedance vs frequency were employed to extract equivalent circuit parameters. Despite the differences in composition the pulsed and CW films displayed similar ionic conductivities, with values of ϳ6 ϫ 10 −10 and ϳ2 ϫ 10 −10 S/cm for H + and Li + , respectively. However, the pulsed PECVD films displayed dramatically reduced electrical leakage. The ratio of ion/ electron conductivity exceeded 100 for pulsed PECVD films, while ion / e was Ͻ1 in CW material.

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