Atomic layer deposition of an HfO 2 thin film using Hf(O-iPr) 4

Abstract

A thin film of hafnium dioxide (HfO 2) was formed on the surface of Si(100) by atomic layer deposition (ALD) using Hf(O-iPr) 4 (Hf(OCH(CH 3) 2) 4, hafnium tetrakis- iso-propoxide) as an Hf source and O 2 as an oxidant. The temperature window of the process was 250–350 °C, which is about 100 °C lower than that of a process using Hf(O-tBu) 4 as a source. This result was in accordance with the decomposition characteristics of the Hf precursor, as investigated by the temperature-programmed decomposition of the compound in an ultra-high vacuum and by thermogravimetric analysis in air. The thickness of a film deposited under the above conditions increased in proportion to the ALD cycles, indicating that the film-growth rate per cycle remained nearly constant during the process. The deposited film consisted of a monoclinic crystal phase included in an amorphous matrix, which was confirmed by X-ray diffraction. The film showed an equivalent-oxide thickness (EOT) of 2.1 nm and a leakage current density of 8.9 × 10 − 6 A/cm 2 at − 1 V. The leakage current was three orders of magnitude lower than that of SiO 2 with the same EOT.