Materials Science Reports最新文献

Ion beam technologies have made tremendous gains in the commercial sector over the past two decades. The ion implantation of semiconductors rapidly became an accepted technology in the 1970s because of its ability to produce superior electronic devices or devices unobtainable by any other process. Ion beam modification of non-semiconductor materials for enhancing surface sensitive properties has been actively pursued in the international R&D community since the mid 1970s and continues to find selected industrial applications. This review briefly describes the status of ion implantation, ion beam mixing, and ion cluster beam deposition technologies and the directions in which they are currently being pursued. The hybrid use of ion beams in conjunction with physical vapor deposition, commonly termed ion beam assisted deposition (IBAD), combines many of the attributes of these ion beam treatments and conventional coating technologies. These include high density, superior adhesion, and the ability to produce arbitrarily thick coatings. Perhaps the most important feature of the IBAD technology is the frequently demonstrated ability to control many coatings properties such as morphology, adhesion, stress, as well as stoichiometry. This control is achieved by suitable variation of the relative arrival rates of energetic ions to that of the neutral species, as well as by control of substrate temperature. Many of these energetic ion effects on thin film formation are described and recent examples of research in the areas of: metastable compound formation, optical and electronic coatings, and tribological and corrosion-resistant coatings are presented. The review concludes with a description of pertinent equipment and an assessment of required future research and commercialization possibilities.

Damage formation and annealing behavior in ion-implanted silicon (Si) have been reported in two different regimes. First, the features of generated defects in ion-implanted submicron Si areas are described, particularly emphasizing changes in the spatial distribution of damage with a reduction in pattern sizes into which implantations are carried out. The results are compared with those obtained by focused ion beam (FIB) implantation in Si. The FIB implanted areas are necessarily doped with a high-density ion current 10³–10⁶ times higher than that in conventional implantation. Therefore, such a high-dose-rate implantation effect induces situations different from those encountered in the conventional method. Second, damage creation and its characteristic behavior with annealing are described for high-energy (1–3 MeV) ion-implanted Si. Specific annealing behaviors of defects are clarified in the temperature ranges between 500 and 1300°C, based on whether or not buried amorphous layers are formed in the implanted regions. The density reduction and configuration changes of defects between furnace annealing and rapid thermal annealing are compared. Also, the effect of bulk material nature (CZ or FZ) on defect growth is discussed in terms of interactions between oxygen atoms in CZ Si and defects. This interaction phenomenon is useful for gettering of metallic impurities harmful for device performance in Si.

Epitaxial silicides belong to a special class of silicides which exhibit a definite orientation relationship with respect to the silicon substrate. A silicide is expected to grow epitaxially on silicon if the crystal structures are similar and the lattice mismatch between them is small. The impetus for the study of epitaxial silicides mainly stemmed from several favorable characteristics of epitaxial silicides in comparison with their polycrystalline counterparts. It now appears that almost all transition-metal silicides can be grown epitaxially to a certain extent on silicon. In this report, theories for the epitaxial growth of silicides are first discussed. The formation and characterization of epitaxial silicides by different techniques are described. Epitaxial growth in various metal/Si systems is summarized. Several recent developments in the growth of transition-metal silicides on silicon are described. Factors influencing the growth of epitaxy are examined. Properties and device applications of epitaxial silicides are addressed.

The thermodynamic and kinetic aspects of ion-irradiation-induced phase transformations in intermetallic compounds are reviewed. The different mechanisms for supplying the thermodynamic driving force for such transformations are discussed. The free energy of an irradiated material can be gradually elevated above that of a metastable state by the accumulation of lattice damage through the production of vacancy—interstitial defects, anti-site defects, and dislocations, or quickly elevated by the formation of a thermal spike in the collision cascade. The final state of the irradiated material will ultimately be determined by kinetic constraints in its transformation to lower-energy metastable and equilibrium states.

The ion-beam-induced epitaxial crystallization (IBIEC) and planar amorphization of amorphous Si (a-Si) layers onto single-crystal Si substrates is reviewed. In particular, the dependence of the process on substrate temperature, on substrate orientation and on the energy deposited by the impinging ions into electronic and elastic collisions is treated in detail and discussed. Emphasis is also given to the influence of impurities on IBIEC, where a variety of different phenomena are observed. For instance, fast diffusers, such as Au, are seen to be swept by the moving c-a boundary and present intriguing segregation profiles. Slow diffusers such as As or O, on the other hand, have not enough mobility to move over long-range distances even in the presence of irradiation, but they can strongly modify the kinetics of IBIEC. Dopants such as B, P and As, for example, enhance the ion-induced growth rate by a factor of 2–3, while O retards it. It is also shown that by decreasing the substrate temperature (or by increasing the ion flux) IBIEC can be reversed resulting in a planar layer-by-layer amorphization. This phenomenon evidences the unique non-equilibrium features of ion-assisted phase transitions in silicon which are the result of a dynamic balance between defect production rate and defect annihilation rate. These data are discussed, mainly in comparison with the purely thermally activated growth of a-Si and a possible explanation of the observed phenomena is presented in terms of a simple model. Finally, new possible applications of the phenomenon, such as the ion-induced regrowth of deposited Si layers and of deposited GeSi heterostructures, are illustrated, demonstrating the high potentialities of ion-beam processing in producing epitaxial layers in a non-conventional manner.

A thermodynamic approach to atomic diffusion in a thermal spike is reviewed. The approach is based on recent ion mixing experiments which demonstrate the influence of the heat of mixing and the cohesive energy of solids on ion mixing. These thermodynamic effects are assimilated into a phenomenological model of ion mixing. The model is generalized to low-energy ion mixing during sputter depth profiling and is used to elucidate the nature of atomic diffusion in a thermal spike. The onset of radiation-enhanced diffusion in ion mixing is also discussed. A fractal geometry approach to spike formation is presented. An “idealized” collision cascade constructed from the inverse-power potential V(r) ∝ r^−1/m (0 < m ≤ 1) is shown to have a fractal tree structure with a fractal dimension D = 1/2m. The same fractal dimension can also be derived from the Winterbon-Sigmund-Sanders (WSS) theory of atomic collisions in solids. The fractal dimension is shown to increase as an actual collision cascade evolves, because of the change of the effective interaction potentials. The concept of “space-filling” fractals is used to specify spikes. The formation of local spikes, their energy densities, the probability of local spikes overlapping, and the time evolution of a collision cascade are also investigated. It is shown that spikes are not expected to form in a single-component solid consisting of elements with atomic number less than 20; many-body collisions have little effect on the formation of spikes; and, the similarity between high-and low-energy ion mixing is the result of the fractal nature of collision cascades.

The use of X-ray and neutron reflectivity to study polymers in the condensed state and in solutions is revieved in this article. Basic theoretical and experimental concepts of specular reflectivity are presented. Research in the application of neutron and X-ray reflectivity is discussed along with the relevance of these studies to important issues in polymer science. These include investigations of ordered and disordered homopolymers and block copolymers in solution and in the condensed state. Finally, a discussion of off-specular, diffuse scattering is presented with its potential use in polymer science.