Texture, Twinning, and Metastable “Tetragonal” Phase in Ultrathin Films of HfO[sub 2] on a Si Substrate

Abstract

Thin HfO 2 films grown on the lightly oxidised surface of (100) Si wafers have been examined using dark-field transmission electron microscopy and selected area electron diffraction in plan view. The polycrystalline film has a grain size of the order of 100 nm and many of the grains show evidence of twinning on (110) and (001) planes. Diffraction studies showed that the film had a strong [110] out-of-plane texture, and that a tiny volume fraction of a metastable (possibly tetragonal) phase was retained. The reasons for the texture, twinning and the retention of the metastable phase are discussed.

Atomic Structure of Domain and Interphase Boundaries in Ferroelectric HfO2

“…Twining also occurs on (001) m (Supporting Information, Figure S1a) and (100) m (Supporting Information, Figure S1b). These twin planes are in good agreement with various reports of twinning configurations identified in toughened zirconia ceramics, 34 HfO 2 thin films grown directly on Si, 35 and in Hf-rich Hf x Zr 1−x O 2 nanocrystals. 36 Twinning is associated with the tetragonal to monoclinic martensitic phase transformation.…”

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

“…Interestingly the kinetics of this phase transformation are also not typical of the martensitic and athermal processes known to occur in bulk HfO 2 13314344. In the bulk, the transformation mechanism is a diffusionless process, in which bond angles and distances rearrange without disrupting atomic connectivity, and this mechanism should therefore produce an abrupt change in lattice parameters that propagates across the entire crystal44.…”

Stabilizing metastable tetragonal HfO2 using a non-hydrolytic solution-phase route: ligand exchange as a means of controlling particle size

“… 24 However, the polydispersity and relatively poor crystallinity of the particles obtained by these methods implies that the obtained samples almost always contain only minor proportions of tetragonal phases and a clear delineation of a size-dependent phase diagram has thus far not been possible. Several instances of stabilizing tetragonal domains have also been reported for thin films of HfO 2 prepared by methods such as atomic layer deposition in a low-oxygen environment, 25 ultra-thin films deposited onto clean Si (100) surfaces by atomic layer deposition, 26 and ion-beam-assisted deposition in an oxygen deficient ambient. 27 Again, the films usually contain mixtures of multiple crystalline and amorphous phases and exhibit considerable heterogeneity in terms of the dimensions of individual domains.…”