The authors investigated the modified atomic layer deposition (ALD) of RuO2 films using bis(ethylcyclopentadienyl)ruthenium [Ru(EtCp)2] at a deposition temperature of 265°C. Oxygen gas diluted with argon was supplied throughout all of the ALD steps. The growth rate of the modified ALD RuO2 was about 1.4Å∕cycle, which is higher than that of conventional Ru ALD due to the increase in the amount of Ru(EtCp)2 adsorption per cycle, as well as the difference in the unit cell volumes of Ru and RuO2. The film thickness increased linearly with the number of cycles, and the incubation cycle in the initial stage was negligible.
Atomic layer deposition ͑ALD͒ has become an essential technique for fabricating nano-scale thin films in the microelectronics industry, and its applications have been extended to multicomponent thin films, as well as to single metal oxide and nitride films. A mathematical film growth model for ALD is proposed to predict the deposition characteristics of multicomponent thin films grown mainly in the transient regime, where the film thickness varies nonlinearly with the number of cycles. The nonlinear behavior of the growth rate and the composition of multicomponent thin films deposited by ALD depend on the precursor used and adsorbing surface. Hence, the equations to describe the change of surface coverage with precursor adsorption and the surface reaction are derived. The area reduction ratio is introduced as a parameter related to the number of adsorbed precursor molecules per unit area. The proposed model was applied to the deposition of Sr-Ti-O thin films to confirm its validity. SrO and TiO 2 films were grown separately to investigate their ALD characteristics and to extract model parameters. As a result, it was shown that the thickness and composition of Sr-Ti-O films follow the trend predicted by the proposed model.
The dielectric constant depending on the film thickness for SrTiO3 films formed on Ru was investigated after an annealing step at 600°C, which shows that the dielectric constant increased abruptly with the film thickness up to 20nm and then increased slightly, remaining relatively constant at a value of about 65. The abrupt increase was due to the crystallinity of SrTiO3 films. On the other hand, the slight increase was related to the existence of nonstoichiometric region near the interface of SrTiO3 film and Ru, which was intermixed with SrTiO3 and Ti–O phases having an equivalent oxide thickness over 0.32nm.
The dielectric properties of SrTiO 3 thin films deposited on SrRuO 3 seed layer were investigated. The SrTiO 3 thin films were deposited by plasma-enhanced atomic layer deposition using Sr͑C 11 H 19 O 2 ͒ 2 and Ti͑O i -C 3 H 7 ͒ 4 as precursors and O 2 plasma as an oxidant. The SrRuO 3 seed layer was formed through deposition of an SrO layer on a RuO 2 substrate and postannealing in O 2 ambient. As a result of introducing SrRuO 3 seed layers, the dielectric constant of 10 nm thick SrTiO 3 thin films increased to 83 compared with that of 16 and 50 for film deposited on Ru directly and seed formed on Ru substrate, respectively.Of the various high-k materials that are candidate capacitor dielectrics in next-generation dynamic random access memory ͑DRAM͒ devices, strontium titanate ͑SrTiO 3 ͒ has attracted interest due to its high dielectric constant ͑k bulk Ϸ 300͒ 1-4 with a paraelectric phase in the normal range of operating temperatures, high breakdown strength, 5 and good chemical stability. 6 For the application of SrTiO 3 films to the capacitor dielectric in DRAM devices, it is necessary to fabricate stoichiometric SrTiO 3 thin films with a thickness of around 10 nm with a suitable thickness and good compositional conformality. However, in an applicable thickness range for a DRAM capacitor, the dielectric constant of the SrTiO 3 thin film decreases abruptly when the thickness decreases due to inadequate crystallinity. 7-10 For enhancement of the dielectric properties of SrTiO 3 films, a strontium ruthenate ͑SRO͒ layer, which is formed by the deposition of an ultrathin SrO layer on Ru and postannealing in N 2 ambient, was introduced as a seed layer in our previous report. 11 As a conductive oxide material, SrRuO 3 has a pseudocubic perovskite structure with a lattice constant of 3.93 Å. Furthermore, the lattice mismatch between SrTiO 3 and SrRuO 3 is roughly 0.5% ͑whereas the lattice constant of perovskite SrTiO 3 is 3.91 Å͒. 12 The thin SRO layer can consequently act as a crystallization seed layer. However, it was hard to confirm the formation of the SrRuO 3 phase by X-ray diffraction ͑XRD͒ analysis, even if the dielectric properties of SrTiO 3 thin films were improved by the introduction of a SRO layer on a Ru substrate. Moreover, it was observed that the Sr-Ru-O layer that formed after annealing tends toward nonuniformity. If the RuO 2 layer is used as the substrate instead of Ru, a sufficient oxygen supply might be possible for the transformation of the deposited SrO to the SrRuO 3 layer ͑SrO + RuO 2 → SrRuO 3 ͒ and the O 2 ambient annealing could also be used instead of N 2 ambient annealing for the crystallization of SrTiO 3 thin films. Thus, in this paper, the SrRuO 3 is introduced as a crystallization seed layer formed by the deposition of a SrO layer on a RuO 2 substrate followed by O 2 annealing, instead of on a Ru substrate followed by N 2 annealing. The dielectric properties of SrTiO 3 thin films deposited on a seed layer are investigated in comparison with those deposited on Ru and on a seed layer ...
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