Hafnium oxide-based dielectrics by atomic layer deposition

摘要

In 2007 there was an important change in the architecture of nanotransistors - the building blocks of modern logic and memory devices. This change was from utilising thermally grown silicon dioxide as a dielectric to so-called high-_ hafnium oxide dielectrics grown by atomic layer deposition. The _rst production logic devices of this era used a hafnium oxide dielectric layer deposited by thermal atomic layer deposition; using HfCl4 and H2O as the precursors. Present day fabrication makes use of hafnium oxide-based atomic-layer-deposited dielectric _lms. The latest nanotransistor devices utilise a third generation hafnium oxide-based dielectric material. This thesis examines hafnium oxide-based thin _lm dielectric materials prepared by thermal atomic layer deposition on silicon substrates. Speci_cally the enhancement of the dielectric response of hafnium oxide by the addition of other elements is examined. Two ternary materials systems were deposited by thermal atomic layer deposition and analysed: titanium-hafnium oxide and cerium-hafnium oxide. Hafnium oxide _lms were deposited to be used as measurement benchmarks. Cerium oxide _lms were also deposited and analysed in their own right as potential dielectric layers. The hafnium oxide and both ternary deposition experiments used (MeCp)2Hf(OMe)(Me) as the hafnium precursor. The titanium-hafnium oxide growth used Ti(iOPr)4 as a titanium source and the cerium oxide and cerium-hafnium oxide work utilised Ce(mmp)4 as a cerium source. Post-deposition specimen sets consisted of an as-deposited sample, a sample spike-annealed in N2 at 850 _C and a sample annealed for 30 minutes at 500 _C. These annealing regimes were performed to mimic typical gate-_rst and gate-last transistor processing steps. The compositions and thicknesses of the _lms were measured using medium energy ion scattering. The structure of the _lms was analysed by X-ray di_raction and Raman spectroscopy. Capacitance-voltage and current density- _eld measurements were taken from fabricated MOS capacitor specimens to assess the dielectric response of the _lms. X-ray di_raction and Raman measurements showed that un-doped HfO2 had monoclinic crystallinity as-deposited and after the two annealing regimes. The dielectric constant and leakage current density, 17 and 1.7_10