Robert Elliman

Investigation of Pt/Ti bilayer metallization on silicon for ferroelectric thin film integration

The stabilities of Pt/Ti bilayer metallizations in an oxidizing atmosphere have been investigated with several thicknesses of interfacial Ti‐bonding layers. Reactions in the Pt/Ti/SiO2/Si interface were examined as a function of various annealing conditions in the temperature range 200–800 °C by using Rutherford backscattering spectrometry, Auger electron spectroscopy, x‐ray diffraction, and transmission electron microscopy. Thermal treatment in oxygen was found to cause rapid oxidation of the Ti layer, accompanied by the migration of Ti into the Pt film. Diffusion of oxygen through the Pt grain boundaries was mainly responsible for the adverse reactions at the interface and loss of mechanical integrity. Thin Ti (10 nm) layers resulted in the depletion of the interfacial bonding layer causing serious adhesion problems, whereas thicker Ti films (100 nm) caused the formation of TiO2−x in the Pt‐grain boundaries, ultimately encapsulating the Pt surface with an insulating TiO2 layer. Improved stability and ad...

Ion-beam-induced crystallization and amorphization of silicon

Thin amorphous silicon layers can be produced in crystalline silicon substrates by ion-implantation. Subsequent ion-irradiation at elevated temperatures can induce such layers to either crystallize epitaxially or increase in thickness, layer by layer. This paper examines these processes and their dependence on substrate temperature and ion-irradiation parameters. It is shown that both processes, epitaxial crystallization and layer-by-layer amorphization, are controlled by ion-beam induced defect production at, or near, the crystalline/amorphous interface. The competition between defect production (determined by the ion flux and rate of nuclear energy deposition) and dynamic defect annealing (determined by the substrate temperature) is shown to play an important role in determining whether the layer crystallizes or amorphizes. Possible models for the observed behavior are discussed.

Gettering of copper to hydrogen‐induced cavities in silicon

Hydrogen implantation and subsequent thermal annealing is found to result in a well‐defined band of cavities in Si. This band is an extremely efficient gettering layer for Cu which is also introduced into the near surface of Si by ion implantation. Profiling of implanted Cu indicates that ∼95% of an initial 3×1015 cm−2 Cu implant is redistributed following annealing at a temperature of 780 °C from a near‐surface damaged layer to a narrow band of cavities of width ∼1000 A at a depth of ∼1 μm. Furthermore, the Si between the surface and the cavity band is essentially defect‐free and that some cavities contain the bulk Cu3Si phase.

Optically absorbing layers on ion beam modified polymers: A study of their evolution and properties

Abstract Nothwithstanding the well known drastic changes wrought upon the optical properties of ion beam irradiated polymers, no systematic search for the corresponding physical mechanism responsible can be found in the literature. Accordingly, a study was made of the depth profiles of optical absorption in a number of irradiated polymers, using radiation extending in wavelength from the ultraviolet, through the visible, and into the infrared. Work concentrated on the mass and dose (fluence) dependence of absorption for noble gas ions. It is shown that for visible light the shape of the depth absorption profile closely follows the distribution with depth of nuclear energy transfer processes, calculated in the normal fashion. This suggests that the optical absorption itself is directly due to polymer degradation by direct knock-on of atoms from the chains. A pronounced maximum in the dependence of the integrated absorption of visible light on projectile mass occurs for neon ions. Furthermore a similar mass dependence is demonstrated for the “kinematic factor” in nuclear collisions with carbon, thus supporting the direct knock-on hypothesis. Finally, an annealing of the irradiation induced polymer damage — a blackening becoming lighter — is also noted. It is ascribed to a specific photochemical reaction.

Effect of hydrogen on the photoluminescence of Si nanocrystals embedded in a SiO2 matrix

Hydrogen passivation of Si nanocrystals is shown to result in a redshift of photoluminescence (PL) emission spectra, as well as the more commonly observed intensity increase. The shift is reversible, with spectra returning to their unpassivated values as hydrogen is removed from the samples by annealing. The magnitude of the redshift also depends on the implant fluence employed for nanocrystal synthesis, increasing with increasing fluence or particle size. These data are shown to be consistent with a model in which larger crystallites are assumed to contain a greater number of nonradiative defects, i.e., the number of nonradiative defects is assumed to scale with the surface area or volume of a nanocrystal. Hydrogen passivation then results in a disproportionate increase in emission from larger crystallites, giving rise to an apparent redshift in the composite PL emission spectrum.

Amorphization of silicon by elevated temperature ion irradiation

Abstract Despite extensive study into the amorphization of silicon by ion irradiation, a detailed understanding of the mechanisms associated with the process is still not available. This is especially true in the case of elevated temperature irradiations where increased levels of dynamic annealing can balance defect production. By controlling the irradiating ion flux (defect production rate), the temperature at which an amorphous layer first appears has been determined for a specific fluence of ions, ranging in mass from 12 (C) to 132 amu (Xe), over a matrix of two orders of magnitude in ion flux and 320°C in temperature. The apparent activation energies determined from the data span from 0.7 to 1.7 eV and increase as a function of ion mass and, consequently, temperature. Previously interpreted as representing processes controlling the crystalline-to-amorphous phase transition, these values are discussed in terms of a two-stage nucleation-limited amorphization process. Results are presented which indicate, that, in the regime where dynamic defect annealing is significant, the amorphization process is initially limited by the availability of nucleation sites, supplied by stable extended defect structures produced by defect accumulation and, subsequently, by the supply of simple defects to these sites.

Nanostructured ion beam-modified Ge films for high capacity Li ion battery anodes

Nanostructured ion beam-modified Ge electrodes fabricated directly on Ni current collector substrates were found to exhibit excellent specific capacities during electrochemical cycling in half-cell configuration with Li metal for a wide range of cycling rates. Structural characterization revealed that the nanostructured electrodes lose porosity during cycling but maintain excellent electrical contact with the metallic current collector substrate. These results suggest that nanostructured Ge electrodes have great promise for use as high performance Li ion battery anodes.

Substitutional solid solubility limits during solid phase epitaxy of ion implanted (100) silicon

High resolution channeling techniques have been used to investigate the maximum nonequilibrium solid solubility which can be achieved during low‐temperature (⩽600 °C) epitaxial regrowth of high‐dose antimony and indium implanted (100) silicon. The substitutional impurity concentration is observed to increase with implant dose and saturate at a limiting concentration well above the maximum equilibrium solid solubility for antimony or indium in silicon. Observed correlations between the measured solubility limits, epitaxial regrowth rates, and intriguing impurity redistribution effects suggest that impurity size and attendant lattice strain at the crystal‐amorphous interface may determine the substitutional solubility limit for low‐temperature annealing, where impurity diffusion lengths are negligible during the time of epitaxial recrystallization.

Thin‐film adhesion changes induced by electron irradiation

The adhesion of thin films of gold, sputter deposited onto silicon, is shown to be improved by subsequent irradiation with 5–30‐keV electrons. The similarities between electron and heavy ion irradiation effects suggest a common (electronic) origin for the change in interfacial bonding.

Impurity‐stimulated crystallization and diffusion in amorphous silicon

An amorphous‐to‐polycrystalline silicon transformation and concomitant In redistribution have been observed in In‐implanted silicon at temperatures well below those at which solid phase epitaxial growth or random crystallization is observed in undoped films. The process is extremely rapid and exhibits a strong dependence on both In concentration and temperature. It is proposed that the In redistribution and accompanying silicon crystallization are mediated by molten, In‐rich precipitates in amorphous silicon.