Preparation of Lithium Containing Oxides by the Solid State Reaction of Atomic Layer Deposited Thin Films

Lithium containing multicomponent oxides are important materials for both lithium-ion batteries and optical applications. In most cases thin films of these materials are desired. Atomic layer deposition (ALD) is a thin film deposition method that is known to deposit high quality films by sequential self-limiting surface reactions. However, the reactivity of lithium ions during the deposition process can pose challenges for the control of the film growth and even destroy the self-limiting nature of ALD completely. In this paper, we have studied the combination of atomic layer deposition and solid state reactions for the generation of lithium containing multicomponent oxide films. Atomic layer deposited transition metal oxide thin films were covered with ALD-grown lithium carbonate, and the films were annealed to produce lithium tantalate, titanate, and niobate. Lithium carbonate was chosen as the source of lithium because it is easy to deposit by ALD and can be handled in air. The films were analyzed as-deposited and after annealing using grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FESEM), and time-of-flight elastic recoil detection analysis (ToF-ERDA). By this method we were able to produce crystalline and very close to stoichiometric films of LiTaO₃, Li₂TiO₃, and LiNbO₃. The films showed only small amounts of carbon and hydrogen impurities after annealing. After prolonged annealing at high temperatures, lithium silicates began to form as a result of lithium ions reacting with the silicon substrates

Cycloheptatrienyl-Cyclopentadienyl Heteroleptic Precursors for Atomic Layer Deposition of Group 4 Oxide Thin Films

Atomic layer deposition (ALD) processes for the growth of ZrO₂ and TiO₂ were developed using novel precursors. The novel processes were based on cycloheptatrienyl (CHT, -C₇H₇) – cyclopentadienyl (Cp, -C₅H₅) compounds of Zr and Ti, offering improved thermal stability and purity of the deposited oxide films. The Cp^MeZrCHT/O₃ ALD process yielded high growth rate (0.7–0.8 Å/cycle) over a wide growth temperature range (300–450 °C) and diminutive impurity levels in the deposited polycrystalline films. Growth temperatures exceeding 400 °C caused partial decomposition of the precursor. Low capacitance equivalent thickness (0.8 nm) with low leakage current density was achieved. In the case of Ti, the novel precursor, namely CpTiCHT, together with ozone as the oxygen source yielded films with low impurity levels and a strong tendency to form the desired rutile phase upon annealing at rather low temperatures. In addition, the thermal stability of the CpTiCHT precursor is higher compared to the usually applied ALD precursors of Ti. The introduction of this new ALD precursor family offers a basis for further improving the ALD processes of group 4 oxide containing thin films for a wide range of applications