T.C.Q. Noakes

Characterization by medium energy ion scattering of damage and dopant profiles produced by ultrashallow B and As implants into Si at different temperatures

High depth resolution medium energy ion scattering (MEIS) has been used to examine the influence of dynamic defect annealing on the damage formed in silicon substrates irradiated with ultralow energy ions (1 keV B+, 2.5 keV As+). Samples were implanted to doses ranging from 3×1014 to 2×1016 cm−2 at sample temperatures −150/−120, 25, and 300 °C. For all doses examined, B implantation at 25 and 300 °C produced a near-surface disordered layer 3–4 nm thick. For doses above 1×1015 cm−2, a second, deeper damaged layer was resolved at a depth greater than the peak of the projected range (Rp) of the implanted ions. For irradiations at −150 °C, MEIS and transmission electron microscope studies indicated the formation of a continuous amorphous layer, extending from the deeper damage region to the surface. However, epitaxial regrowth of this layer was not complete after a 30 s anneal at 600 °C, being arrested near Rp by clusters containing B. The dependence of B transient enhanced diffusion on the implant temperatur...

Structure determination of the and surface alloy phases by medium-energy ion scattering

The substitutional surface alloy phases and have been investigated by medium-energy ion scattering (MEIS) using 100 keV ions. Blocking patterns in the scattered ion yield have been measured for and incidence geometries. Simulations of these blocking patterns have been performed for a range of trial structures and the optimum values of the structural parameters obtained are compared with those available from earlier low-energy electron diffraction (LEED) and photoelectron diffraction (PhD) investigations. The MEIS results confirm the presence of rumpling in the outermost alloy layer, with corrugation amplitudes of and for the CuMn and CuAu surface alloys respectively. This result supports the previously reported anomalously large corrugation for which has been attributed to the local high-spin state of the Mn atoms.

Electrical, structural, and chemical properties of HfO2 films formed by electron beam evaporation

High dielectric constant hafnium oxide films were formed by electron beam (e-beam) evaporation on HF last terminated silicon (100) wafers. We report on the influence of low energy argon plasma ( ∼ 70 eV) and oxygen flow rate on the electrical, chemical, and structural properties of metal-insulator-silicon structures incorporating these e-beam deposited HfO2 films. The use of the film-densifying low energy argon plasma during the deposition results in an increase in the equivalent oxide thickness (EOT) values. We employ high resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and medium energy ion scattering experiments to investigate and understand the mechanisms leading to the EOT increase. We demonstrate very good agreement between the interfacial silicon oxide thicknesses derived independently from XPS and HRTEM measurements. We find that the e-beam evaporation technique enabled us to control the SiOx interfacial layer thickness down to ∼ 6 A. Very low leakage current density (<10−4 A/cm2) is measured at flatband voltage +1 V into accumulation for an estimated EOT of 10.9±0.1 A. Based on a combined HRTEM and capacitance-voltage (CV) analysis, employing a quantum-mechanical CV fitting procedure, we determine the dielectric constant (k) of HfO2 films, and associated interfacial SiOx layers, formed under various processing conditions. The k values are found to be 21.2 for HfO2 and 6.3 for the thinnest ( ∼ 6 A) SiOx interfacial layer. The cross-wafer variations in the physical and electrical properties of the HfO2 films are presented.

Morphology of enriched alloy layers in an anodized Al–Cu alloy

Using medium energy ion scattering, combined with Rutherford backscattering spectroscopy, transmission electron microscopy and atomic force microscopy, the development of the copper-enriched alloy layer during anodizing of a sputtering-deposited Al–0.4 at.% Cu alloy has been examined. The enriched layer is located just beneath the amorphous alumina film that is produced on the anodized alloy. Importantly for understanding the mechanism of formation of the enriched layer, the layer is revealed to be of thickness ∼2.1 nm from the start of the anodizing, when enrichment of copper is very low, with no significant increase in the thickness of the layer as the copper enriches to ∼3×1015 Cu atoms cm−2, the maximum measured in the present experiments. The findings are consistent with a model of the layer in which the copper is present mainly in copper-rich clusters.

Surface and sub-surface segregation at the Pt25Rh75(111) surface: a medium energy ion scattering study

Using 100 keV incident He+ ions, medium energy ion scattering (MEIS) has been used to determine the layer-by-layer composition of the outermost three atomic layers of a Pt25Rh75(1 1 1) crystal after annealing to temperatures in the range 900–1300 K. Highly layer-specific compositional information was obtained using three different double-alignment scattering geometries, although full analysis of the data included simulation of blocking curves recorded around the double alignment geometry. The results provide independent confirmation of the conclusions of an earlier quantitative low energy electron diffraction (LEED) investigation of the same crystal, notably strong Pt segregation to the outermost layer, enhanced average Pt segregation with increasing temperature, and Pt depletion of the second layer. MEIS also confirms the presence of a weak rumpling of the outermost atomic layer, with Pt atoms lying at slightly larger layer spacing than the surrounding Rh atoms. The quantitative agreement is significantly better than in the only previous comparison of LEED and MEIS for the determination of layer-dependent alloy surface segregation. Possible reasons for anomalously large surface vibrational amplitudes are discussed.

Effect of Copper Enrichment on the Electrochemical Potential of Binary Al-Cu Alloys

Using Al-Cu alloys, containing between 0.1 and 26 atom % Cu, deposited by magnetron sputtering and etching in sodium hydroxide solution, enrichments of copper have been developed selectively in the alloys. Rutherford backscattering spectroscopy and medium energy ion scattering quantified the enrichments and their locations just beneath the alumina-based oxides remaining from the etching. In some cases, the enrichment was sufficient for oxidation of copper to take place; in other cases, it was not, so that only aluminum was oxidized, with copper being confined to the alloy, enriching in an alloy layer about 2 nm thick. The potentials of the etched alloys in 0.1 M ammonium pentaborate solution at 293 K increased as the copper content of the enriched alloy layer increased. The enrichment of copper in the alloy beneath an alumina-based film free of copper species, i.e., without requirement for oxidation of copper and incorporation of copper species into the oxide, was sufficient to generate increases in potential of similar magnitude to those found for specimens in which oxidation of copper had taken place. The potential increased by ∼410 mV with an increase in the level of enrichment to Cu atoms

Characterization of hafnium aluminate gate dielectrics deposited by liquid injection metalorganic chemical vapor deposition

Thin films of hafnium aluminate, with varying aluminum content, have been deposited by liquid injection metalorganic chemical vapor deposition using the metal alkoxide precursors hafnium methyl-methoxy-propanolate and aluminum iso-propoxide. X-ray diffraction analysis showed that the films were amorphous at aluminum concentrations above 7 at. %. Postdeposition annealing indicated that the oxide-transition temperature from amorphous to crystalline increased with aluminum content. Medium-energy ion scattering showed that up to 900 °C, internal oxidation of the silicon substrate had been inhibited. The capacitance–voltage characteristics of the films significantly improved following annealing in dry air.

Behavior of Impurity and Minor Alloying Elements during Surface Treatments of Aluminum

The behavior of impurity and minor elements during electropolishing, chemical polishing, and anodizing treatments is examined for 99.99% Al and Al-0.2 atom % Mn alloy containing iron, copper, and silicon impurities in the parts per million range. Copper is enriched strongly, to at least 2-4 × 10 14 copper atoms cm -2 , during the two polishing treatments. Assuming that the copper is located in a metal layer of thickness I nm, just beneath the surface film, the enrichment corresponds to an average concentration of about 5 atom % copper. In contrast, iron and silicon impurities were not enriched significantly by the various treatments. Manganese was enriched in the Al-0.2 atom % Mn alloy to about 7 × 10 14 atoms cm -2 , Manganese appeared to interact with copper impurity in the alloy to reduce the level of copper enrichment. The factors determining the degree of enrichment include the Gibbs free energies per equivalent for formation of the various impurity and alloying element oxides, interactions between coenriching elements, and the location of the particular atoms in the metal, especially the proportions of the atoms in solid solution, in fine particulates, and segregated at cellular and grain boundaries.

Anodic film growth in the Al–Ta alloy system

The ionic transport numbers, relative migration rates of cation species and formation ratios are reported for barrier anodic films formed on metastable, solid solution Al–Ta alloys, with compositions extending from the aluminium-rich to the tantalum-rich ends of the system. The data were obtained by marker experiments, using ion implanted xenon, transmission electron microscopy, Rutherford backscattering spectroscopy and medium energy ion scattering. The films are amorphous and form by migration of metal and oxygen species. The ionic transport numbers and the formation ratios depend approximately linearly upon the composition of the alloy, between the values for anodic alumina and anodic tantala. The migration rate of Al3+ ions exceeds that of Ta5+ ions, but reduces in relative magnitude as the tantalum content of film increases. The faster migration of Al3+ ions is consistent with the higher energy of the Ta5+–O bond compared with that of the Al3+–O bond. Due to the difference in mobilities of the cation species, the films comprise an outer layer of alumina and an inner layer containing units of both alumina and tantala. The two-layered films can develop fingers of inner layer oxide that penetrate the outer alumina layer due to the higher ionic resistivity of the alumina. Such channelling of current can lead to mixing of inner layer oxide and alumina and thereby hinder formation of an alumina layer, particularly in films on the more tantalum-rich alloys.

Chemical interface analysis of as grown HfO2 ultrathin films on SiO2

The quality of the interface between a HfO2 high-k gate dielectric and the Si substrate directly influences its electrical properties. The chemical composition of the interfacial region of HfO2 deposited on a SiO2∕Si(100) substrate by pulsed liquid injection metal organic chemical vapor deposition at 430 and 550°C was investigated by medium energy ion scattering, angular resolved x-ray photoemission spectroscopy analysis, and high resolution transmission electron microscopy. It is shown that the HfO2∕SiO2 interface is abrupt with low roughness and no silicate. The interface roughness with SiO2 is found to be close to that generally measured in silicon technology (silicon oxide above silicon substrates) [E. A. Irene, Solid-State Electron., 45, 1207 (2001)]. The analysis of the experimental results indicates that the deposition technique does not lead to the formation of an extended silicate layer at the HfO2∕SiO2 interface.