Growth and structure control of HfO2−x films with cubic and tetragonal structures obtained by ion beam assisted deposition

Abstract

Hafnium oxide films were grown by ion beam assisted deposition on water-cooled Si (100) substrates, under conditions of oxygen starvation, using hafnium vapor and an oxygen ion beam. The transport ratio (TR), i.e., the ratio between the arrival rate of hafnium to that of oxygen, was varied between 0.5 and 10, and ion energy was varied between 1 and 20 keV. The films were analyzed using x-ray diffraction and x-ray photoelectron spectroscopy. Films having the CaF2 cubic structure with a lattice parameter of about 0.512 nm were repeatedly obtained. In addition, at 20 keV ion energy and TR values of 4 and above, films with a tetragonal structure were obtained. The latter structure, believed to be a distortion of the cubic structure, has a c/a ratio of 1.01 and its space group is considered to be different from the high temperature tetragonal HfO2 structure. The new tetragonal structure also presents high Knoop hardness, with values between 15 and 25 GPa. Substrate rotation speed was found to affect the structure and the orientation of the films. All films exhibit a stoichiometry in the vicinity of HfO1.6, with the tetragonal films apparently being Hf2O3. These structures are attributed to a very fast cooling rate during film formation. Films deposited without substrate water cooling, or with substrate heating up to 500 °C contain a large component of the monoclinic phase. The new cubic and tetragonal structures are stable at room temperature and upon annealing up to 450 °C in vacuum, but convert to the monoclinic structure upon annealing at 500 °C in air, indicating that their low oxygen content is a key factor for their stability.

Growth of Dysprosium‐, Scandium‐, and Hafnium‐based Third Generation High‐κ Dielectrics by Atomic Vapor Deposition

“…However, a consistent indexation of the observed peaks can be achieved by assuming a cubic structure as is shown in Figure 8. Assuming a HfO 2 -like structure, the peak indexation is as shown in Figure 8 and the lattice parameter of (Dy 0.5 Hf 0.5 ) 4 O 7 is 5.155 Å, whereas that of (Sc 0.5 Hf 0.5 ) 4 O 7 would be 5.012 Å, close to cubic HfO 2 (5.12 Å [28] ); assuming a bixbyite structure (like Dy 2 O 3 and Sc 2 O 3 ) all indices in Figure 8 should be double [e.g., (222) instead of (111)] and the lattice parameters will also double. The relative difference in lattice parameters agrees with the fact that Dy 2 O 3 (10.665 Å) has a larger lattice parameter than Sc 2 O 3 (9.845 Å).…”

Microstructure and interfaces of HfO2 thin films grown on silicon substrates

“…Under some special conditions, such as thin film deposition, polymorphs can exist. In the films grown by atomic layer deposition and annealed at 500-700 C, high-temperature tetragonal [17] and cubic [18,19] phases were observed. However, the final microstructure depends on both the starting deposition temperature and the annealing temperature [20].…”

Real-time atomistic observation of structural phase transformations in individual hafnia nanorods

“…HfO 2 is isomorphic to ZrO 2 (refs 13, 14), and the two oxides have similar lattice parameters and the same space group in each phase. Insight may be gleaned, therefore, from examining the case of ZrO 2 , which has been successfully stabilized in the tetragonal phase at room temperature in nanocrystalline form71213. This represents a suppression of the ZrO 2 transition temperature by over 1000 °C from its bulk value of 1050 °C (refs 16, 17, 18, 19).…”