Hf Layer Research Articles

Retarded Growth of Sputtered HfO2 Films on Germanium

ABSTRACTHfO2 films were deposited by reactive sputtering on Ge and Si substrates simultaneously, and we found not only the interface layer but the HfO2 film was thinner on Ge substrate compared with that on Si substrate. A metallic Hf layer has a crucial role for the thickness differences of both interface layer and HfO2 film, since those thickness differences were observed only when an ultrathin metallic Hf layer was predeposited before HfO2 film deposition. The role of metallic Hf is understandable by assuming a formation of volatile Hf-Ge-O ternary compounds at the early stage of film growth. These results show an advantage of HfO2/Ge over HfO2/Si systems from the viewpoint of further scaling of electrical equivalent thickness of the gate oxide films.

Retarded Growth of Sputtered HfO2 Films on Germanium

ABSTRACTHfO2 films were deposited by reactive sputtering on Ge and Si substrates simultaneously, and we found not only the interface layer but the HfO2 film was thinner on Ge substrate compared with that on Si substrate. A metallic Hf layer has a crucial role for the thickness differences of both interface layer and HfO2 film, since those thickness differences were observed only when an ultrathin metallic Hf layer was predeposited before HfO2 film deposition. The role of metallic Hf is understandable by assuming a formation of volatile Hf-Ge-O ternary compounds at the early stage of film growth. These results show an advantage of HfO2/Ge over HfO2/Si systems from the viewpoint of further scaling of electrical equivalent thickness of the gate oxide films.

Formation of interfacial layer during reactive sputtering of hafnium oxide

Hafnium oxide is one of the most promising high dielectric constant materials to replace silicon dioxide as the gate dielectric. To take the advantages of high dielectric constant of HfO2 thoroughly, the relatively low dielectric constant interfacial layer must be controlled carefully. In this work, the formation of an interfacial SiO2 layer at the HfO2/Si interface was studied comprehensively. It is observed that during reactive sputtering deposition of the HfO2 layer, a very thick interfacial SiO2 layer, thicker than 3 nm, would be grown. O-radical signals, instead of O2-radicl signals, are detected in the sputtering chamber. An O-radical enhanced oxidation model is proposed to explain such an unusual thick SiO2 layer. The adoption of a two-step deposition method, the thickness of interfacial SiO2 layer can be reduced only if the bottom Hf layer is thicker than 5 nm. However, the reduction of effective oxide thickness would be limited. Reoxidation of Hf film sounds a better choice. A 1.0–1.5-nm-thick interfacial SiO2 layer is still observed. This implies that the traced oxygen in the sputtering chamber plays a critical role on the formation of the interfacial layer. It is thus concluded that reactive sputtering is not a suitable method to prepare a HfO2 layer with a negligible interfacial SiO2 layer. Reoxidation of Hf film is a better choice, but the oxygen content in the sputtering chamber must be well controlled.

Impact of Hf Metal Predeposition on the Properties of HfO2 Grown by Physical and Chemical Vapor Deposition

Electrical and microstructural properties of a hafnium oxide (HfO2) grown by physical vapor deposition (PVD) and chemical vapor deposition (CVD) onto a predeposited hafnium metal (Hf) are investigated. In PVD in an Ar/O2 plasma atmosphere, energetic oxygen species oxidize the Si substrate through HfO2, generating a thick interfacial layer between the HfO2 and Si substrates. The interfacial layer, however, is found to be controllable to have a minimum equivalent oxide thickness (EOT) and lower leakage current by the predeposition of Hf metal due to the blocking of oxygen diffusion into the Si substrate by the oxidation of Hf metal itself. In addition to the oxygen blocking, the CVD-grown HfO2 films on the predeposited Hf metal layer are improved due to the easy dissociation of the Hf precursor on the metallic Hf layer with a shorter incubation time. The leakage current with the predeposited Hf metal is two orders of magnitude lower than that on the Si substrate, whereas the EOT and the interfacial layer thickness are invariant.

Interface Formation and Electrical Properties of TiOxNy/HfO2/Si Structure

In this work, interface formation and electrical properties of the interface between TiOxNy and HfO2 for application of gate structure were investigated as a function of annealing temperature. HfO2 layers were formed at 500°C by the thermal oxidation of the sputter-deposited Hf layers on n-Si (001) and followed by reactive DC magnetron sputter deposition of TiOxNy layers at room temperature. Phase identification of TiOxNy layers before and after thermal annealing of TiOxNy(100 nm)/HfO2/Si by X-ray diffraction (XRD) indicates the formation of TiO1-zNz with the preferential orientations in (111), (200) and (220) directions. Depth profiling analysis of Ti, Si, Hf, N, and O element for TiOxNy(50 nm)/HfO2/Si structure by Auger electron spectroscopy (AES) shows the increased oxidation of TiOxNy layers at elevated annealing temperature, TA = 800°C. Investigation of the interfacial reaction of TiOxNy(5 nm)/HfO2 by depth profiling using X-ray photoelectron spectroscopy (XPS) shows the existence of mixture of TiO1-zNz and TiO2 (or TiO) phase and increased fraction of TiO2 phase and Hf–O bondings for the samples annealed at the elevated annealing temperature, TA = 800°C. Sheet resistance of TiOxNy/HfO2/Si systems measured by a four-point probe shows the initial decrease in RS values but the abrupt increase in RS values at TA = 800°C. The combined results indicate that TiOxNy layer acts as an effective diffusion barrier for Hf and O element in the HfO2 layer at the annealing temperature ≤700°C, but O and Hf diffused out of the HfO2 layers reacted with TiOxNy layers at the elevated annealing temperature of 800°C.

Characterization and control of the HfO2/Si(001) interfaces

The HfO2/Si(001) interfaces formed by reactive dc sputter deposition of Hf buffer layer followed by HfO2 stacking were analyzed by high-resolution transmission electron microscopy, medium energy ion scattering (MEIS), and photoelectron spectroscopy using synchrotron-radiation lights. The present MEIS analysis determined the elemental depth profiles and revealed that no Hf buffer layer resulted in growth of SiO2 at the interface, and that the presence of the Hf layer led to the formation of Si-rich silicate-like interlayers. The binding energy shifts of Si-2p3/2 identified the chemical bonds of the interfacial layers and confirmed the formation of SiO2 (no buffer layer) and silicate layers (presence of the buffer layers) at the interfaces. The Hf-buffer layer suppresses the O diffusion toward the interface and thus the thicker the buffer layer, the thinner the Hf-silicate interlayer. The deposition condition of HfO2 (1.3 nm)/Hf (1.3 nm) has achieved the highest permittivity of 28 for HfO2 (3.6 nm) and 8 for the silicate layer (1.7 nm).

Reduced temperature and bias-voltage dependence of the magnetoresistance in magnetic tunnel junctions with Hf-inserted Al2O3 barrier

A modified tunnel barrier structure for the magnetic tunnel junction (MTJ) was fabricated by inserting a Hf layer in the middle of the Al2O3 tunnel barrier. MTJs with the Hf-inserted barrier show a higher tunnel mangnetoresistance (TMR) ratio and weaker temperature and bias-voltage dependence of TMR compared to the MTJs with a conventional Al2O3 barrier. The enhancement of the TMR ratio and the reduction of the temperature and bias-voltage dependence were attributed to the reduction of defects in the barrier.

Enhanced tunnel magnetoresistance by hf-layer insertion in the AlO/sub x/ tunnel barriers

Summary form only given. Magnetic tunnel junctions consist of two ferromagnetic electrodes separated by an insulating barrier. The tunnel magnetoresistance(TMR) and junction resistance critically depend on the insulating layer quality. The defects in tunnel barrier or at the interfaces between barrier and metal electrodes could degrade MR ratio by introducing spin flip scattering. In this study, we have introduced the artificial modification of the oxide barrier by forming Hf oxide in the middle of the Al/sub 2/O/sub 3/ barrier. As Hf oxide has higher heat of formation (-268kcal/mole of Hf) than Al oxide (-202kcal/mole), the inserted Hf layer could act as oxide stabilizer and decrease the degree of disorder and defects in the barrier. Magnetic tunnel junctions of Hf(5nm)/NiFe(8nm)/IrMn(20nm)/CoFe(4nm)/Al oxide or Al-HfAl oxide/CoFe(3nm)/NiFe(15nm) were deposited by magnetron sputtering system. Tunnel barriers were formed by exposing the Al(1.4nm) layer or Al-Hf-Al(0.6/0.2/0.6nm) layer to ozone and oxygen mixture gas for tens of minutes.

Synthesis and crystal structure of the α polytype of HfNBr

α -HfNBr has been prepared at 760 °C in a sealed evacuated fused silica tube by reaction between NH 4 Br and Hf followed by purification through chemical vapour transport under a temperature gradient. The crystal structure of this compound at room temperature has been determined for the first time by Rietveld refinement of X-ray powder diffraction data, electron diffraction and high resolution electron microscopy. It crystallises in the orthorhombic space group Pmmn with the unit cell parameters a =4.1165(2), b =3.5609(2), c =8.6440(3) Å. α -HfNBr is isotypic to FeOCl and is built from layers of composition BrHfNNHfBr stacked along c that are separated by a Van der Waals gap. The hafnium atoms are six-coordinated by four nitrogen atoms and two bromine atoms. The resulting coordination polyhedron may be described as a highly distorted octahedron. Electron diffraction and high resolution electron microscopy studies reveal that the material is almost free of defects in the inner part of the crystals and confirm the structural model refined by the Rietveld method. Graphic

Solid State Amorphisation Reaction in Evaporated Hf/Ag Multilayer Films

The perturbed angular correlation technique (PAC) was applied to observe the interdiffusion in Hf/Ag multilayers. Sample with 10 Ag layers of 40 Å intercalated with Hf layers of 100 Å was implanted with 111In probes or irradiated with thermal neutrons in order to achieve the presence of the radioactive PAC probes 111In or 181Hf, respectively. A solid state reaction caused by thermal diffusion led to the formation of an amorphous structure in the investigated samples.

Growth of Hf and HfN on GaN by molecular beam epitaxy

Hf and HfN thin films were grown on n-type GaN(0001̄) by molecular beam epitaxy using a custom built Hf electron beam source and an ammonia leak. The films were characterized by reflection high-energy electron diffraction (RHEED) and atomic force microscopy. It was found that epitaxial growth of Hf is possible even at room temperature. GaN films varying in thickness from 0.6 to 1.8 μm were grown on c-plane sapphire, using ammonia as a precursor, to serve as substrates. Then the films were annealed in ammonia as the temperature was lowered in order to produce a N termination. Hf was then deposited on top of the GaN at temperatures between 20 and 730 °C, both with and without ammonia incident on the sample. Deposition of pure Hf at room temperature revealed an epitaxial two-dimensional (2D) (although with some three-dimensional character) RHEED pattern with sixfold symmetry. The surface is reconstructed with a (2×2) R30° structure. We propose that the pattern is rotated 30° with respect to that of the substrate GaN because of a HfN interlayer between the GaN and Hf layers. When the films were annealed in vacuum up to 730 °C, the 2D pattern became more transmission like. If Hf was deposited at substrate temperatures of 350 °C and higher, a diffraction pattern corresponding to that of a polycrystalline material was observed.

Microstructure and magnetic behaviors of Fe/Hf multilayers by vapor deposition

Electron beam vapor deposition was employed to prepare Fe/Hf multilayers. The thickness, periodicity, chemical composition, microstructure and magnetic properties of the films were characterized and measured by various methods. It was found that the Fe layer could grow in an amorphous structure when the Fe layer thickness t Fe⩽2.2 nm and the Hf layer thickness 1.8 nm⩽t Hf ⩽13.2 nm. The magnetic moment per Fe atom in Fe/Hf multilayers reduced considerably with forming amorphous Fe when Hf was fixed at 13.2 nm. For the Fe/Hf multilayers with amorphous Fe, the magnetic moment per Fe atom changed strongly with the thickness of constituent metals. Possible mechanism responsible for these observations are also discussed.

Structural analysis of the HfB 2(0001) surface by impact-collision ion scattering spectroscopy

The structure of the hafnium diboride (0001) surface was studied by impact-collision ion scattering spectroscopy. It was found that the clean surface, which is terminated by a flat (1×1) Hf layer at room temperature, turns into a surface with Hf adatoms after heating over 2000°C. This is probably caused by desorption of boron from the subsurface.

Improvement of surface properties by modification and alloying with high-power ion beams

Surface treatment and alloying experiments with Al, Fe, and Ti-based metals as well as Si wafers were conducted on the Repetitive High Energy Pulsed Power-I (RHEPP-I) accelerator [0.8 MV, 20 Ω, 80 ns full width at half maximum (FWHM) pulse width, up to 1 Hz repetition rate] at Sandia National Laboratories. Ions are generated by the magnetically confined anode plasma (MAP) gas-breakdown active anode, which can yield a number of different beam species including H, C, N, O, Kr, and Xe, depending upon the injected gas. Enhanced hardness and wear resistance have been produced by treatment of 440C stainless steel, by the mixing of a thin-film Pt coating into Ti-6Al-4V alloy, and of a Si coating into Al 6061-T6 alloy (Al-1.0Mg-0.6Si). Mixing of a thin-film Hf layer into Al 6061-T6 has improved its corrosion resistance by as much as four orders of magnitude in electrochemical testing, compared with untreated and uncoated Al6061. Processing of Si was used to validate simulation codes. When treated with nitrogen ions, melt and full epitaxial growth was observed to depths of 4–6 μm. Experiments are ongoing to further understand the microstructural basis for these surface improvements.

HfNixP – Intercalation of Ni into the Three‐Dimensional Compound HfP

AbstractThe new compound HfNixP (x = 0.426(1), crystal structure: P63/mmc, a = 3.737(1) Å, c = 12.666(2) Å, V = 153.21(7) Å3) has been prepared by arc‐melting of HfP with nickel and subsequent annealing at 1400°C. Its crystal structure can be considered as a filled HfP structure, with the Ni atoms inserted into the trigonal prismatic voids of the Hf sublattice. Since the neighboring trigonal Hf6 prisms are centered by P atoms, each of the three rectangular faces of the Hf6Ni prism is capped with one P atom. Altogether, the structure of HfNixP consists of alternating layers of Hf atoms with the packing sequence AABB. One P and the Ni position are situated between the eclipsed Hf layers, whereas the other P site between the A and B layers is surrounded by six Hf atoms in a staggered arrangement. The calculated density of states (Extended Hückel approximation) points to metallic conductivity; threedimensional metallic behavior is assumed because of the Hf–Hf bonding interactions along all three directions.

Multilayered Ni/Hf and solid-state amorphization studied using the slow positron beam technique

A monoenergetic slow positron beam was used to profile thin Ni/Hf multilayers. We measured the changes in the S-parameter of the Doppler broadened positron annihilation radiation through the solid-state amorphization. It is shown that a high density of vacancy-type defects in Hf layers strongly induces the fast diffusion of Ni atoms.

Studies of multilayers of Cu-Hf with a variable-energy positron beam

We report on the results of depth-profiling experiments of multilayers of Cu-Hf using a slow position beam. Experimental data reveal that the Hf layers contain many open-volume type defects and that there might be thin oxidized Hf that reduces theS parameter in the interfaces between Cu-Hf.

The oxidation process and dissipation factor of Al/Ta/Hf multilayered anodized thin‐film capacitors

AbstractIt is known that the anodic oxidation of Hf proceeds by the diffusion of anions into Hf thin film and is affected by the other overlayered films existing on Hf in multilayered anodized thin‐film capacitors. to characterize multilayered thin oxide film structures necessary for the fabrication of high‐quality capacitors, a correlation between dissipation factor and oxidation process has been investigated as a function of anodization voltage and thinfilm thicknesses of Al/Ta/Hf and Ta/Al/Hf multilayers.The results indicate that thin‐film capacitors with low dissipation factor can be obtained by anodizing Al/Ta/Hf thin films so long as their original multilayered structures are maintained during anodization and the Ta intermediate layer acts as a transport medium of oxygen ions for the bottom Hf layer. With increasing anodization voltage, Ta ions migrate toward the surface of the multilayer, which alters the original multilayered structure and contributes to higher dissipation factor.When the intermediate layer is Al such as in the case of Ta/Al/Hf multilayer capacitors, the flow of oxygen ions to the bottom Hf layer is restricted during anodization by the formation of an oxidized Al layer and this makes the dissipation factor higher. It has been concluded that in order to fabricate thin‐film capacitors with low dissipation factor, it is vital to have the presence of an intermediate layer such as Ta which has a lower heat of formation for oxidation than Hf.

Cross-sectional transmission electron microscopy study for Nb/AlOx-Al/Nb, Nb/ZrOx-Zr/Nb, and Nb/HfOx-Hf/Nb Josephson junctions

We studied the interfaces of Nb Josephson junctions with an overlayer structure using cross-sectional transmission electron microscopy. We compared Nb/AlOx-Al/Nb, Nb/ZrOx-Zr/Nb, and Nb/HfOx-Hf/Nb junctions. The interface between the Zr layer and Nb base electrode, and that between the Hf layer and Nb were smoother than that between the Al layer and Nb. The roughness of the interface between Al and Nb is caused not by the roughness of the original Nb base electrode but grain boundary diffusion following Al deposition. Annealing increased the roughness of the interface between Al and Nb, but had very little effects on the interfaces between Zr and Nb, or Hf and Nb. We attribute these effects to the differences in the melting points of the various overlayers.

Cu-Hf multilayers studied by slow positron beam and time differential perturbed angular correlation

Time differential perturbed angular correlation (TDPAC) and monoenergetic positron beam measurements of the Cu-Hf multilayers have been performed. The structural disorder and the remarkable strain in Hf layers of the multilayer are discussed from the microscopic point of view.