Oxygen Self-Diffusion inHfO2Studied by Electron Spectroscopy

Abstract

High-resolution measurement of the energy of electrons backscattered from oxygen atoms makes it possible to distinguish between (18)O and (16)O isotopes as the energy of elastically scattered electrons depends on the mass of the scattering atom. Here we show that this approach is suitable for measuring oxygen self-diffusion in HfO2 using a Hf(16)O2 (20 nm)/Hf(18)O2 bilayers (60 nm). The mean depth probed (for which the total path length equals the inelastic mean free path) is either 5 or 15 nm in our experiment, depending on the geometry used. Before annealing, the elastic peak from O is thus mainly due to electrons scattered from (16)O in the outer layer, while after annealing the signal from (18)O increases due to diffusion from the underlying Hf(18)O2 layer. For high annealing temperatures the observed interdiffusion is consistent with an activation energy of 1 eV, but at lower temperatures interdiffusion decreases with increasing annealing time. We interpret this to be a consequence of defects, present in the layers early on and enhancing the oxygen diffusivity, disappearing during the annealing process.

Ion migration in crystalline and amorphous HfOX

“…In a MOSFET or ReRAM device, HfO x films can-depending on the processing procedures-be either crystalline or amorphous, and hence it is necessary to understand ion transport in both phases and to elucidate the similarities and differences in behavior. Ion transport, in contrast to electronic transport, 1 in HfO x has only been examined in a few publications, however (in crystalline phases [2][3][4][5] and in the amorphous state [6][7][8][9], and no general picture of the behavior has as yet emerged.…”

Advanced techniques for characterization of ion beam modified materials

“…A recently developed technique, electron Rutherford backscattering spectrometry [32][33][34], has demonstrated its analytical power that is complementary to other surface analysis techniques, including RBS, medium energy ion scattering (MEIS), X-ray photoemission spectroscopy (XPS), and secondary ion mass spectrometry (SIMS).…”

“…Electrons that have scattered inelastically as well as elastically contain information on the electronic structure. Since the small recoil energy losses from the e-beam energies are far below the displacement energies to create irradiationinduced defects and the electronic excitations resulting from the modest current densities (typically at $25 lA cm À2 ) are usually too low to cause sample decomposition, eRBS can also be applied to investigate irradiation-induced or thermally-activated selfdiffusion within the surface region or at the interfaces [34].…”

On the Atomic Kinetic Energies in Ceramic Oxides

“…In ECS on the other hand, electrons are scattered from all atomic constituents of the target. Hence, a reliable extraction of the mean kinetic energy of the Hf atoms becomes problematic due to lack of knowledge of the exact shape of the Hf elastic peak [35].…”

“…Altogether, [35] In cases where only the total VDOS is available, the use of Equation (1) yields the average kinetic energy <KE> per atom of the compound, which is valuable for testing the ECS measured values. By combining the measured INS low [37] and high [38] phonon frequencies of v-SiO 2 at room temperature, <KE> = 63.9 meV is deduced which agrees with the average measured ECS values of α-Silica, Finally, it may be seen that Ke(X) in oxides systematically decreases with increasing mass of X.…”