Ion implantation is widely used for doping semiconductors at low concentration, but, with the advent of a new generation of high current implanters, synthesizing new materials rather that simply doping them has become feasible. This technique has been successfully applied to fabricating silicon-on-insulator (SOI) structures with oxygen and nitrogen for several years. Since we are interested in understanding the mechanisms of formation of these layers, we have concentrated on sub-stoichiometric implantation doses of oxygen where it is easier to observe the coalescing layer. In order to determine whether this process of compound formation is more general, our studies were expanded to include implantation of the transition metals. Here, elevated substrate temperatures are necessary to minimize Si surface damage. The resulting disilicide layers are of remarkably high quality: they are single crystals in registry with the silicon wafer and they have better residual resistivities than comparable UHV-reacted silicides.

High temperature annealing of Simox wafers (T > 1300°C), has been proved to dramaticaly increase the quality of the SOI structure.

The heat treatment leads to a redistribution of the implanted oxygen, opposite to its concentration profile, towards the buried layer.

This paper describes from a thermodynamical point of view the SiO2 precipitates dissolution. The physical mechanisms of the oxygen migration are also discussed.

Near-surface compositional modification of ion-bombarded alloys results from the dynamic interplay of several atomistic processes. In addition to displacement mixing leading to t randomization of atomic locations, which is dominant at relatively low temperatures, and preferential loss of alloying elements by sputtering, many thermally-activated processes, including radiation-enhanced diffusion, radiation-induced segregation and Gibbsian adsorption, also play important roles. The relative contributions of these processes to the evolution of the target composition profile depends on the target materials and irradiation variables. Although a good understanding of the individual processes has been achieved, information regarding their synergistic effects on alloy surface modification is still limited. In the present article, these processes will be characterized in simple physical terms, and the present understanding of their relative significance and contributions in changing the target composition during ion bombardment will be discussed in view of recent progress in theoretical modeling and experimental study.

The Aluminum-rich end of the Al-Cr-Er ternary system was investigated in an effort to find new quasicrystalline alloys. Composition, dose dependence and substrate temperatures during ion irradiation were varied. A quasicrystal alloy with the Al-Cr intensity pattern was found at low Er content. Another phase was observed that did not index to any known equilibrium structure. This new phase has d spacings and diffraction line intensities which are similar to those of the Al-Li-Cu quasicrystalline phase.

Transmission electron microscopy (TEN) and Brillouin scattering methods were used to determine the lattice dilatation and shear elastic constant as a function of the degree of long-range order during room temperature irradiation of Zr3Al with 1.0-MeV Kr+. The results indicate that the onset of amorphization in Zr3Al is triggered by an elastic shear instability, and that the instability is directly related to the volume dilatation associated with the destruction of long-range order. It is also shown that the volume dependence of the shear elastic constant associated with radiation-induced disordering and amorphization is virtually identical to that associated with the heating to melting of many metals.

CuTi was irradiated with 1MeV Ne+ and Kr+ at various temperatures in the Argonne-HVEM interfaced to a tandem accelerator. The integrated intensity of diffuse ring was measured by a microdensitometer and analyzed by Gibbons model for the dose dependence of the amorphous volume. The results indicate that the direct amorphization occurs in a single damage zone with Kr+, but the overlapping of three damage zones is necessary with Ne+. The critical temperature for amorphization was 401±22K for Ne+ and 543±20K for Kr+, respectively. With Kr+, the critical temperature was nearly equal to the thermal crystallization temperature of an amorphous zone embedded in the crystalline matrix. Using the present observations, the relation between the amorphization process and the critical temperature is discussed.

The amorphous phaseformation in Ti-Si bilayers upon ion mixing at elevated temperatures and in Ti-Si multilayers upon thermal treatment was studied. In the case of ion mixing with 5×1015 cm−2 Xe atoms at temperatures around 240°C a 100nm thick amorphous Ti-Si alloy is formed with a very homogeneous Ti:Si=3 :4 composition. Thermal treatment of the Ti-Si multilayer structure at similar temperatures also yields amorphous silicide layers. The results are interpreted according to the evolution in a planar binary diffusion couple, where the Si and Ti concentrations in the reacted layer are dictated by thermodynamic and kinetic arguments.

Au/Zr bilayer films with inert-gas markers were produced by low energy (< 4 keV) implantation. Mass transport was measured during ion-beam mixing with 1 MeV Kr at several temperatures between 330 and 540K. Two distinct regimes of apparent Arrhenius behavior were found with activation enthalpies of 0.06 and 0.9 eV in the temperature range 330–440K and 460–540K, respectively. Microstructural changes during ion-beam mixing were studied in situ, in a high voltage electron microscope. Heterogeneous nucleation of an amorphous phase was observed during mixing. The results are compared with similar studies reported previously in Ni/Zr bilayer specimens.

Interfacial reactions induced by ion beam mixing and furnace annealing in Al/Mo bilayers are investigated. The amount of interfacial ion m'xing, 4Dt, follows a linear dose dependence for irradiation temperatures ≤80 C. Below room temperature, the mixing efficiency, defined as d(4Dt)/dø, is temperature independent, and agrees fairly well with the prediction of the phenomenological model based on chemically biased diffusion in thermal spike. We conclude that thermal spike mixing dominates for Xe irradiation of Al/Mo at low temperatures. The mixing efficiency becomes temperature-dependent above room temperature with an apparent activation enthalpy of about 0.17±0.02eV. A layer of 15–20 at.% Mo forms by ion mixing, while oAl12 Mo forms upon thermal annealing in a nonuniform fashion starting at 500°C. Reaction of Mo with large-grained Al substrates shows the same nonuniform characteristics as in evaporated Al/Mo bilayers, implying a minor role of grain boundary effects. Oxygen gettered in the Mo film could be an important factor that influences the interfacial reaction.

The triode sputtering technique and a “split-target” arrangement were used to produce metastable crystalline and amorphous phases in the Cu-W system under essentially oxygen-free conditions. Large metastable extensions of solid solubility were observed both from the Cu (fcc) and W (bcc) sides of the phase diagram, and a wide range of metallic glass formation was observed, approximately between 30 and 65 at.% W. The thickness of the amorphous Cu-W phase (40–160 pm) that can be deposited without the formation of the metastable bcc phase appears to be dependent on the Cu-W alloy composition. On heating, the crystallization temperature of the amorphous alloys was higher than 350°C. The behavior of the lattice parameter and near-neighbor distance has been studied with x-ray diffraction, showing small positive deviations from an assumed Vegard's Law. Hardness measurements indicate that the metastable crystalline phases are relatively harder than the amorphous phase.

We have measured the radiation-enhanced diffusion of Au in amorphous Si in the temperature range 77–700 K. Gold was implanted to depths of 500Å at concentrations of an atomic %. The samples were than amorphized to depths of -2μm using MeV Ar implants at liquid nitrogen temperature. Radiation-enhanced diffusion was induced by a 2.5 MeV Ar beam at doses of 2×1016−2×1017/cm2 and dose rates of 7×1012−7×1013/cm2sec. The diffusion coefficients show three well defined regions. At temperatures <400K diffusion is essentially athermal and due to ballistic mixing. At temperatures between 400K and 700K the diffusion, which is considerably enhanced over the usual thermal values, has an Arrhenius behavior with an activation energy of 0.37 eV. At higher temperatures thermal diffusion, with an activation energy of 1.42 eV, dominates.

Interfacial reactions of titanium thin films on P+-implanted silicon have been studied by transmission electron microscopy.

The presence of titanium thin films on P+-implanted silicon was found to alter the defect configuration in the recrystallized layer. Interfacial reactions of titanium thin films on silicon were also found to be influenced by the presence of dopants as well as changes in the microstructures of the substrate. The results are compared with those found in previous studies of Ti thin films on ion-implanted silicon as well as on unimplanted samples. The mechanisms for the chaiiges in defect configuration and phase formation are discussed.

The self-alignment of the Co-Si interaction at the edge of a Si-SiO2 transition has previously been ascribed to the fact that Co is the main moving species during silicide formation. However, the reactions in the Co-Si system are more complex. The phenomena of lateral silicidation and encroachment are therefore investigated at various stages of the Co/Si reaction using samples starting either from sputtered Co layers or from cosputtered Co-Si multilayers with varying average stoichiometries. The mechanisms resulting in the absence of lateral silicidation are clarified.

A comprehensive study of MeV-15N-ion-implanted InP by a variety of analytical techniques has revealed the physical processes involved in MeV ion implantation into III-V compound semiconductors as well as the influence of post-implantation annealing. It provides a coherent picture of implant distribution, structural transition, crystalline damage, and lattice strain in InP crystals induced by ion implantation and thermal annealing. The experimental results from the different measurements are summarized in this report. Mechanisms of amorphization by implantation and recrystallization through annealing in MeV-ion-implanted InP are proposed and discussed in light of the results obtained.

Indium implantation into a-axis sapphire to peak concentrations of 8–45 mol % In produces amorphous surface layers.Migration of In during isothermal annealing at 600°C shows a strong ion dose dependence. For a dose of 6×1016In/cm2, two distinct types of In migration are seen - a) rapid diffusion of In within amorphous Al2O3 and b) diffusion of In into crystalline Al2O3 underlying the amorphous layer. For doses lower than 3×1016In/cm2 , no such migration of In is seen under identical anneal conditions. However, In undergoes phase separation into crystalline In2O3 particles embedded in amorphous Al2O3 at all doses.

Single crystals of α-Al2O3 were implanted with 57Fe+ at room temperature to fluences ranging from 1016 to 1017 ions/cm2. The damage in the implanted zone and the valence states and local environment of implanted ions were studied by transmission electron microscopy, Rutherford backscattering-channelling, and conversion electron Mössbauer spectroscopy. The implanted iron was distributed among the three charge states Fe2+, Fe3+, and Fe°(metallic clusters) with the relative amount of each varying with concentration of implanted iron.

The bombardment of solid surfaces with ions in the energy range below about 150 eV, depending on the ion-substrate combination, results in a net growth of material on the surface. An ion beam facility capable of producing highly uniform, low energy beams of current densities in the range 10−2 to 1 Am−2 has been developed to study the potential of this growth technique for the fabrication of thin epitaxial films at low temperatures.

The energy deposition associated with ion bombardment, which is considered to be responsible for the low temperature epitaxy capability, can also cause atomic displacements on the surface and near-surface regions of the substrate during initial growth and in the growing film. A study of the growth processes thus requires investigation of the damaging effects of low energy ion bombardment. In the present paper, fundamental aspects of the implantation and deposition of materials using very low energy ions will be discussed.

Low-energy (50 eV) homoepitaxial beam deposition of silicon is simulated using many-body silicon potentials and molecular dynamics techniques. Results are presented for the case of a 50 eV neutral silicon beam incident on the (2×1) dimer reconstructed Si(100) surface. The beam is aligned along (110) symmetry directions, which are the most natural channeling directions in the silicon lattice. Roughly 10% of the incident beam atoms are scattered from the surface with a small fraction of their initial energy. About half of the incident atoms penetrate the lattice, but scatter strongly and come to rest within 10–15Å of the surface. The remainder are steered accurately into the bulk (110) channels, where they penetrate some 30–100 Å into the lattice. Those atoms which do not undergo bulk channeling cause considerable lattice damage to the near-surface (depth ≥10Å) region.

Many-body forces obtained by the Embedded-Atom Method (EAM) [41 are incorporated into the description of low energy collisions and surface ejection processes in molecular dynamics simulations of sputtering from metal targets. Bombardments of small, single crystal Cu targets (400–500 atoms) in three different orientations ({100}, {110}, {111}) by 5 keV Ar+ ions have been simulated. The results are compared to simulations using purely pair-wise additive interactions. Significant differences in the spectra of ejected atoms are found.

Although NiO(100) sputters congruently at 300 K under 2 keV argon ion flux, sputter reduction is observed above a substrate threshold of 350 K. The reduction kinetics are described quantitatively by Fickian diffusion of subsurface oxygen coupled to differential sputtering at the sample surface. Two additional surface oxygen species are detected on sputter reduced NiO by XPS and these species have not been found on either stoichiometric or chemically reduced NiO(100).

CoO(100) also shows sputter reduction, although only surfaces that have been pre-annealed to 973 K show significant reduction. Under these conditions, an epitaxial layer of Co3 O4 forms on the CoO substrate and this layer has a threshold temperature to sputter reduction of 550 K. Reduction kinetics for the epitaxy appear similar to those of NiO(100).