Atomic Layer Deposition of HfO2 Thin Films Exploiting Novel Cyclopentadienyl Precursors at High Temperatures

Atomic layer deposition (ALD) of HfO 2 thin films was studied using four novel cyclopentadienyl precursors, namely, (CpMe) 2 HfMe 2, Cp 2 Hf(OMe) 2, (CpMe) 2 Hf(OMe)Me, and (CpMe) 2 Hf(OMe) 2 . Ozone was used as the oxygen source. Among the cyclopentadienyl precursors, (CpMe) 2 HfMe 2 and (CpMe) 2 Hf(OMe)Me were the most promising, showing ALD-type growth characteristics at high temperatures as the self-limiting growth mode was confirmed at 400 °C. ALD-type growth was verified also on 60:1 aspect ratio trench structures even at 450 °C, where perfect conformality was obtained. The growth rate stayed nearly constant at around 0.5 Å/cycle at substrate temperatures between 350 and 500 °C. When Cp 2 Hf(OMe) 2 and (CpMe) 2 Hf(OMe) 2 were applied, slight decomposition of the precursor was detected at 350−400 °C, and thus a self-limiting growth mode was not achieved. Time-of-flight elastic recoil detection analyses demonstrated stoichiometric HfO 2 films, where impurity concentrations were below 0.1 at % for C, H, and N in films deposited from each of the four Hf precursors. In addition, thin HfO 2 films showed good dielectric properties such as low hysteresis, nearly ideal flatband voltage, and effective permittivity values similar to previously reported HfO 2 films obtained by the alkylamide-based processes.