Titanium dioxide thin films were grown on RuO 2 layers by atomic layer deposition. The stabilizing effect of the bottom rutile-type RuO 2 layer resulted in growth of the TiO 2 rutile films at temperatures above 275°C. Stabilization of the TiO 2 rutile phase occurred due to local epitaxial growth of the polycrystalline RuO 2 /TiO 2 /RuO 2 structure, as revealed by transmission electron microscopy. A dielectric constant as high as 155 and equivalent oxide thickness ͑EOT͒ as low as 0.5 nm were determined from the capacitance-voltage measurements for the TiO 2 films grown above 275°C. A leakage current density of 10 −3 A/cm 2 at 1 V bias voltage was obtained for the films with EOT equal to 0.5 nm.Titanium dioxide is an attractive dielectric material for microelectronic applications. Depending on its growth conditions, TiO 2 can be most easily prepared in amorphous, anatase, and/or rutile phases. The rutile phase exhibits very high dielectric constant, ranging from 90 to 170, depending on the lattice orientation. 1 Due to the high dielectric constant, the TiO 2 rutile phase is considered a promising material for capacitors in future generations of dynamic random access memories ͑DRAMs͒. 2 Unfortunately, rutile often coexists in thin films with lower dielectric constant TiO 2 phase, i.e., anatase, thereby resulting in a reduction of effective dielectric constant. Postdeposition annealing at temperatures above 800°C has to be performed to obtain pure rutile phase films. 3-5 However, it was shown that the growth of phase-pure rutile films at low temperatures can be stabilized by choice of an appropriate substrate. For instance, by using atomic layer deposition ͑ALD͒ and TiCl 4 and H 2 O as precursors, pure rutile films have been grown on ͑1-102͒-oriented sapphire substrates at 425°C. 6 Recently, Kim, et al. demonstrated ALD growth of TiO 2 rutile film at even lower temperatures on a Ru substrate pretreated by O 3 . 7 This pretreatment of the Ru electrode resulted in a thin surface film of RuO 2 with the structure compatible to that of the TiO 2 rutile phase. Using this approach, TiO 2 films with a dielectric constant of 100 were prepared at temperature as low as 250°C. 8 In a DRAM capacitor dielectric film should be combined with conductive electrodes. As the affinity of TiO 2 is about 4 eV, 9 metals with high work function should be used as electrodes to prevent excessive leakage currents due to Schottky emission. We have recently demonstrated that the work function of ruthenium oxide is more than 5 eV. 10 RuO 2 has high conductivity and crystallizes in the rutile structure with the lattice parameters ͑a RuO 2 = 0.4499 nm, c RuO 2 = 0.3107 nm͒ close to that of the TiO 2 rutile phase ͑a TiO 2 = 0.4593 nm, c TiO 2 = 0.2959 nm͒. Therefore, RuO 2 is a promising material for electrodes in capacitors with TiO 2 dielectric. In our work we have extended the approach of Kim et al. 7 to use RuO 2 as a seed layer for the TiO 2 rutile phase growth. Instead of oxidizing the Ru surface to obtain RuO 2 , we have used bottom polycrysta...

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Capacitor structures with undoped and Al-doped TiO 2 dielectrics grown on RuO 2 electrodes by TiCl 4 -based atomic layer deposition were investigated. In the undoped films, relative permittivity values up to 160 were obtained. The leakage current densities were as low as 3 × 10 −8 and 3 × 10 −7 A cm −2 in the TiO 2 films with capacitance equivalent thicknesses (CETs) of 0.49 and 0.39 nm, respectively, at a voltage of 0.8 V. Al doping of TiO 2 led to a decrease of leakage current as well as permittivity. As a consequence, comparable leakage current densities were obtained for undoped and Al-doped films at similar CET values.

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