Cycloheptatrienyl-cyclopentadienyl heteroleptic precursors for atomic layer deposition of group 4 oxide thin films

Atomic layer deposition (ALD) processes for the growth of ZrO ₂ and TiO ₂ were developed using novel precursors. The novel processes were based on cycloheptatrienyl (CHT, -C ₇H ₇) - cyclopentadienyl (Cp, -C ₅H ₅) compounds of Zr and Ti, offering improved thermal stability and purity of the deposited oxide films. The Cp ^MeZrCHT/O ₃ 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.