Mathematical model for a radioactive marker in silicide formation

A mathematical model is constructed to interpret the profiles of radioactive (^31)Si tracers in a computer simulation proposed by R. Pretorius and A. P. Botha [Thin Solid Films 91, 99 (1982)]. This model assumes that only Si moves in the silicide, that the Si moves interstitially and convectively, and that the moving Si can exchange sites with the stationary Si in the silicide lattice. An analytical solution of this model is given and confirms the published computer simulation data. However, it is shown that the model is physically inadequate. Solutions of another model which assumes that metal, instead of Si, is the moving species for silicide formation (either interstitially, or substitutionally, or both), with self-diffusion of (^31)Si in the silicide during silicide formation. Almost all the experimental data can be fitted by solutions of both models. These examples demonstrate that radioactive tracer experiments alone are insufficient to determine the moving species when a solid binary compound film forms by reaction of adjacent elemental layers. Both inert marker and tracer data are needed to identify the moving species and the mechanisms

A structure marker study for Pd_2Si formation: Pd moves in epitaxial Pd_2Si

A sample with the configuration Si (111)/single crystalline Pd_2Si/polycrystalline Pd_2Si/Pd is used to study the dominant moving species during subsequent Pd_2Si formation by annealing at 275 °C. The interface between monocrystalline and polycrystalline Pd_2Si is used as a marker to monitor the dominant moving species. The result shows that Pd is the dominant moving species in the monocrystal

Effects of ion irradiation on conductivity of CrSi_2 thin films

Electrical resistivity measurements are used to study damage in CrSi_2 thin films induced by Ne, Ar, or Xe ion irradiation over a fluence range of 10^(10)–10^(15) ions cm^(−2). Irradiation produces a factor of 5–12 increase in film conductivity at the higher fluences. The influence of defect generation and recombination is evident. We speculate that formation of a compound defect is a dominant factor enhancing film conductivity. A temperature dependence at low fluences is reported and tentatively identified

Chromium silicide formation by ion mixing

The formation of CrSi_2 by ion mixing was studied as a function of temperature, silicide thickness and irradiated interface. Samples were prepared by annealing evaporated couples of Cr on Si and Si on Cr at 450°C for short times to form Si/CrSi_2/Cr sandwiches. Xenon beams with energies up to 300 keV and fluences up to 8 X 10^15 cm^(-2) were used for mixing at temperatures between 20 and 300°C. Penetrating only the Cr/CrSi_2 interface at temperatures above 150°C induces further growth of the silicide as a uniform stoichiometric layer. The growth rate does not depend on the thickness of the initially formed silicide at least up to a thickness of 150 nm. The amount of growth depends linearly on the density of energy deposited at the interface. The growth is temperature dependent with an apparent activation energy of 0.2 eV. Irradiating only through the Si/CrSi_2 interface does not induce silicide growth. We conclude that the formation of CrSi_2 by ion beam mixing is an interface-limited process and that the limiting reaction occurs at the Cr/CrSi_2 interface

Magnetic properties of amorphous thin films produced by ion mixing

We have produced several magnetic amorphous alloys by ion mixing of thin multilayer films. Our results show that the ion mixing technique is able to produce amorphous films of the various categories (transition metal-metalloid, transition metal pairs) at the composition appropriate for the appearance of magnetic ordering. A comparison of their saturation magnetization with that of related vapor quenched films suggests similar nearest-neighbor coordination in both kinds of samples

Self-consistent determination of the perpendicular strain profile of implanted Si by analysis of x-ray rocking curves

Results of a determination of strain perpendicular to the surface and of the damage in (100) Si single crystals irradiated by 250-keV Ar+ ions at 77 K are presented. Double-crystal x-ray diffraction and dynamical x-ray diffraction theory are used. Trial strain and damage distributions were guided by transmission electron microscope observations and Monte Carlo simulation of ion energy deposition. The perpendicular strain and damage profiles, determined after sequentially removing thin layers of Ar+-implanted Si, were shown to be self-consistent, proving the uniqueness of the deconvolution. Agreement between calculated and experimental rocking curves is obtained with strain and damage distributions which closely follow the shape of the trim simulations from the maximum damage to the end of the ion range but fall off more rapidly than the simulation curve near the surface. Comparison of the trim simulation and the strain profile of Ar+-implanted Si reveals the importance of annealing during and after implantation and the role of complex defects in the final residual strain distribution

Radioactive silicon as a marker in thin-film silicide formation

A new technique using radioactive 31Si (half-life =2.62 h), formed in a nuclear reactor, as a marker for studying silicide formation is described. A few hundred angstroms of radioactive silicon is first deposited onto the silicon substrate, followed immediately by the deposition of a few thousand angstroms of the metal. When the sample is heated, a silicide is first formed with the radioactive silicon. Upon further silicide formation, this band of radioactive silicide can move to the surface of the sample if silicide formation takes place by diffusion of the metal or by silicon substitutional and/or vacancy diffusion. However, if the band of radioactive silicide stays at the silicon substrate interface it can be concluded that silicon diffuses by interstitial and/or grain-boundary diffusion. This technique was tested by studying the formation of Ni2Si on silicon at 330 °C. From a combination of ion-beam sputtering, radioactivity measurement, and Rutherford backscattering it is found that the band of radioactive silicide moves to the surface of the sample during silicide formation. From these results, implanted noble-gas marker studies and the rate dependence of Ni2Si growth on grain size, it is concluded that nickel is the dominant diffusing species during Ni2Si formation, and that it moves by grain-boundary diffusion

Thermal reaction of Al/Ti bilayers with contaminated interface

We have studied some new aspects of thermal reactions in Al/Ti bilayers in which the interface is purposely contaminated with oxygen. After annealing at a temperature of 460 °C, an Al_3Ti compound forms at the interface, moreover some Al diffuses through the Ti to form a compound at the free surface. The amount of aluminum at the free surface can be as large as at the interface. Nucleation and lateral growth of Al_3Ti at the interface are locally unfavorable. This results in a competition between the lateral growth of Al_3Ti at the Al/Ti interface and the diffusion of Al to the free surface. Once full coverage by Al_3Ti is obtained at the Al/Ti interface, the diffusion of Al to the surface becomes negligible