Novel mixed alkylamido-cyclopentadienyl precursors for ALD of ZrO2 thin films

Mixed alkylamido-cyclopentadienyl compounds of zirconium, (RCp)Zr(NMe2)3 (R = H, Me or Et) are introduced as precursors for atomic layer deposition (ALD) of high permittivity zirconium oxide thin films. Ozone was used as the oxygen source. Only slight differences were observed in the ALD growth characteristics between the three liquid precursors. The ALD-type growth mode was verified at 300 deg C with a growth rate of about 0.9 A cycle-1. Good film conformality was observed, as step coverages of 80-90% were measured for films deposited onto high aspect ratio (60 : 1) trenches. As compared to the commonly used Zr(NEtMe)4 precursor, these novel precursors showed comparative volatility and growth rate but higher thermal stability, as well as lower impurity content in the deposited stoichiometric ZrO2 films. The films deposited by the (RCp)Zr(NMe2)3/O3 processes tended to crystallize in the high temperature cubic form even when the film thickness exceeded 50 nm, while the Zr(NEtMe)4/O3 process resulted in films with mixed phases. The cubic phase ensures high permittivity and thus the capacitance equivalent thickness remained extremely low, even below 0.8 nm, with low leakage current density of 10-7 A cm-2 at 1 V when a 6.4 nm ZrO2 film was deposited on TiN.