Ion Beam Mixing Experiments Research Articles

Ion implantation — A modern tool to produce metastable systems

During the last years, ion implantation/irradiation has been more and more recognized to be a versatile tool to produce non-equilibrium systems. In this respect, two experimental procedures can be distinguished. Irradiation of a target with chemically inert ions will result in a highly disordered state, in some cases even in a metastable amorphous phase. Ion beam mixing experiments, where sandwich structures are intermixed by heavy ion irradiation, belong to this class of experiments. Irradiation is contrasted by implantation, where a chemically active species is forced into the sample. Here thermodynamic constraints like solubility on stoichiometry limits can be overcome. Examples will be given for both types of experiments to illustrate the specific advantages of the technique.

Thin film analysis by low energy proton induced X-ray emission

A 100 keV proton beam has been used for measuring the thickness of thin films from the proton energy loss determined by using the energy dependence of the yield of X-rays emitted from a gold backing. Comparison between the proposed method and Rutherford backscattering is shown for erosion, thermal interdiffusion or ion beam mixing experiments with carbon and aluminum-gold films.

In situ rutherford backscattering measurements of ion-beam-induced atomic mixing

An apparatus for ion beam mixing experiments has been developed using the high voltage mass separator (HVMS) at Chalk River Nuclear Laboratories. The system features are: (1) implantation with heavy ions energies up to 2000 keV, followed immediately, and in situ, by RBS analysis using MeV 4He + ions; (2) temperature range from 40 K to 600 K without sacrificing high-quality ion current measurements or high vacuum conditions; (3) as many as 100 independently implanted areas on up to five samples simultaneously in the chamber, plus various calibration standards; and (4) a rotational degree of freedom for detecting orientation effects, and for minimizing their impact.

High Energy Ion Beam Mixing in Al2 O3

ABSTRACTThe ion beam mixing technique has been employed to mix metal atoms into the surface layers of Al2O3. Ion beams of Fe+ and Zr+ in the 1 to 4 MeV energy range were used to irradiate Al2O3 specimens on the surfaces of which films of chromium or zirconium had been evaporated. Some specimens were irradiated at elevated temperatures of 873 or 1173 K. Rutherford backscattering (RBS) and channeling methods were used to measure the metal atom depth profiles near the surface. Analyses of the backscattering data included binary collision calculations using the codes TRIM and MARLOWE. The significance and limitations of high energy (>1 MeV) beams for ion beam mixing experiments is discussed. Evidence was found for radiation enhanced diffusion and/or solubility of zirconium and chromium in Al2O3 at 873 K.

Ion Beam Induced Interfacial Reactions in Molybdenum Thin Films on Silicon

When an energetic ion penetrates through an interface between a thin film (of species A) and a substrate (of species B), ion induced atomic mixing may result in an intermixed region (which contains A and B) near the interface. Most ion beam mixing experiments have been directed toward metal-silicon systems, silicide phases are generally obtained, and they are the same as those formed by thermal treatment.Recent emergence of silicide compound as contact material in silicon microelectronic devices is mainly due to the superiority of the silicide-silicon interface in terms of uniformity and thermal stability. It is of great interest to understand the kinetics of the interfacial reactions to provide insights into the nature of ion beam-solid interactions as well as to explore its practical applications in device technology.About 500 Å thick molybdenum was chemical vapor deposited in hydrogen ambient on (001) n-type silicon wafer with substrate temperature maintained at 650-700°C. Samples were supplied by D. M. Brown of General Electric Research & Development Laboratory, Schenectady, NY.

Pulsed Beams and Ion-Beam Mixing: Metal-Si and Metalmetal Structures

ABSTRACTEnergy deposition and heat-flow determine the temperature distributions in pulsed-beam irradiated structures. In laser irradiated Si, transient conductance measurements indicated a liquid/solid interface velocity of 2.8 m/sec during crystallization in agreement with a heat flow model. With pulsed ionbeam annealing of metal-Si structures, melting starts at the interface; epitaxial NiSi2 layers have been formed. Ion-beammixing experiments on polycrystalline and epitaxial Au-Ag bilayers show that intermixing is more pronounced in the polycrystalline structures as is the case with thermal annealing. Superlattice structures are formed in the epitaxial structures.