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

Heteroleptic Cyclopentadienyl-Amidinate Precursors for Atomic Layer Deposition (ALD) of Y, Pr, Gd, and Dy Oxide Thin Films

Thin films of rare-earth (RE) oxides (Y₂O₃, PrO_<i>x</i>, Gd₂O₃, and Dy₂O₃) were deposited by atomic layer deposition from liquid heteroleptic RE­(<i>ⁱ</i>PrCp)₂(<i>ⁱ</i>Pr-amd) precursors with either water or ozone as the oxygen source. Film thickness, crystallinity, morphology, and composition were studied. Saturation was achieved with Gd₂O₃ when O₃ was used as the oxygen source at 225 °C and with Y₂O₃ with both oxygen sources at as high temperature as 350 °C. The growth rates were 0.90–1.3 Å/cycle for these processes. PrO_<i>x</i> was challenging to deposit with both oxygen sources but with long, 20 s purges after the water pulses uniform films could be deposited. However, saturation was not achieved. With Dy₂O₃, uniform films could be deposited and the Dy­(<i>ⁱ</i>PrCp)₂(<i>ⁱ</i>Pr-amd)/O₃ process was close to saturation at 300 °C. The different oxygen sources had an effect on the crystallinity and impurity contents of the films in all the studied processes. Whether ozone or water was better choice for oxygen source depended on the metal oxide material that was deposited