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

Abstract

Atomic layer deposition (ALD) of HfO2 thin films was studied using four novel cyclopentadienyl precursors, namely, (CpMe)2HfMe2, Cp2Hf(OMe)2, (CpMe)2Hf(OMe)Me, and (CpMe)2Hf(OMe)2. Ozone was used as the oxygen source. Among the cyclopentadienyl precursors, (CpMe)2HfMe2 and (CpMe)2Hf(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 Cp2Hf(OMe)2 and (CpMe)2Hf(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 HfO2 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 HfO2 films showed good dielectric properties such as low hysteresis, nearly ideal flatband voltage, and effective permittivity values similar to previously reported HfO2 films obtained by the alkylamide-based processes.