J. S. Colligon

Analytical modelling of sputter induced surface morphology

Abstract A review is presented of the mathematical treatment of the development of surface topography of amorphous materials bombarded by an energetic beam of particles. In the first section the relevant analytical equations are presented and extended to include surface diffusion. In general the complete analytical approach is shown to be intractable, but in the second section some of the equations are adapted to suit computer programmes which allow calculation of the development of a surface contour provided the original contour and the functional relationship between sputtering coefficient and angle (S(θ)) are specified. Finally, geometrical construction techniques, which allow the topographical development to be predicted, are discussed and a new cursor, which evolves from the appropriate S,θ relationship, is shown to be significantly simpler to use than the erosion slowness curve when making a geometrical construction of the evolving surface.

EQUILIBRIUM TOPOGRAPHY OF SPUTTERED AMORPHOUS SOLIDS. II.

The sputtering of an amorphous solid is considered analytically and the equations of motion of the changing surface topography derived.

Computer calculations of single crystal sputtering by low energy ions

Abstract A study of copper crystal sputtering by 10–2500 eV Ar ions was performed by molecular dynamic computer simulation. Good agreement with experiment was obtained in spatial and energy distributions of sputtered atoms and in energy dependence of sputtering. A sharp peak was observed in energy spectra of atoms moving in the uppermost (001)Cu layer, appearing due to correlated collisions for ion energies E0≤50 eV. The nonmonotonic dependence of average and maximal energy transferred by ions to atoms in (001) layers on the layer number was established. It was found that there is an optimum energy of the incoming ions which gives to the greatest number of atoms in upper layers with energy higher than some chosen threshold.

Dependence of sputtering coefficient on ion dose

Abstract The sputtering coefficient of polycrystalline gold bombarded by 10–40 keV Ar+ ions has been measured as a function of total ion dose and shown to exhibit oscillations in magnitude between 30 and 100%. Possible experimental errors which would give rise to such an oscillation have been considered, but it is apparent that these factors are unable to explain the measurements. It is proposed that a change in the Sublimation Energy associated with either bulk damage or formation of surface topographical features arising during ion bombardment may be responsible for the observed variations in sputtering coefficient.

Variation of the sputtering yield of gold with ion dose

Abstract In an earlier publication1 it was noted that the sputtering yields of gold varied considerably over an initial bombardment period during which approximately 6 × 1016 ions/cm2 struck the target surface; above this dose yields became constant and agreed reasonably well with other sources of data. The present work describes a modified version of the original apparatus which allows up to one hundred experiments to be carried out in one evacuation under better U.H.V. conditions than previously attained. 0–600 eV Nitrogen (N2) ions have been used and, as the present technique allows measurement of total yields as low as 1012 atoms, a careful study of the sputtering yield-dose pattern has been possible. Scanning electron micrographs of the gold surface at various stages of the bombardment indicate only slight surface roughening. A model is proposed based on the development of dislocation loops which could explain the relatively long recovery time in the 600 eV yield which follows a short bombardment at ...

Dynamic study of ion etching in a high resolution SEM

On-line studies of surface topographical development have been made by mounting a saddle-field ion source into a standard scanning electron microscope. Preliminary results obtained during operation in both dynamic and static modes are presented.

Sputtering of graphite-like BN crystals

Abstract The sputtering of hexagonal and rhombohedral forms of boron nitride is studied by computer simulation and experimentally. The sputtering yield of the rhombohedral crystal is found to be up to twice as large as that of the hexagonal one in the energy range of Ar+ ion bombardment from 0.3 to 4 keV. For both types of BN, boron is sputtered more easily than nitrogen. Computer calculated spatial and energy distributions of the particles sputtered from the (0001) face of a BN single crystal are studied. Spatial distributions exhibit preferential sputtering of B and N atoms in particular directions. These atoms form three distinct spots for each of the two components; the patterns for B and N are turned through an angle of 60° with respect to each other. Features of the backward and forward sputtering from a target containing a different number of the (0001) layers, as well as the mechanisms of particles ejection are discussed.

Interaction potential for atoms of magnetic materials

The change in interaction potential of iron and nickel atoms under a magnetic phase transition has been studied. It has been shown that the energy of interaction between atoms increases when spins of the atoms become parallel. For the interaction of two Fe or two Ni atoms with parallel spins, the potential well is deeper, and is shifted towards shorter distances than for the case of random spin orientation. This effect has to be taken into account when explaining a step-like change in sputtering yield of magnetic materials during a magnetic phase transition.

Anomalous sputtering of single crystal ni in close-packed directions at the curie point

Abstract The spatial distribution of particles sputtered from the (001) face of Ni single-crystals is studied as a function of temperature. A significant increase in sputtering intensities both in the (011) directions and in random directions is found experimentally near the Curie point (T c = 635 K). The temperature dependence of mean-square angular deviation ψ2 of sputtered particles from close-packed (011) directions was determined both experimentally and by computer simulation. Except for a near-T c region, ψ2 increases linearly with temperature in agreement with the result of the computer calculation. At the Curie point, the experimental ψ2 has a sharp peak (corresponding to the value of ψ at 1200 K, determined by computer calculations). This result suggests a significant increase in displacement amplitude of surface atoms near T c, and gives a method for its estimation from sputtering patterns.

Secondary ion emission studies of the range profiles of implanted ions

Abstract The apparatus described provides a universal technique for determining the range profiles of any ion species which has been implanted in a target. In this work a previously implanted sample is bombarded in the target chamber of a stainless steel UHV system by a low energy (1 keV) ion beam. Typical beam intensity is 1 μA/cm2 on the target. The resulting sputtering process causes the target surface to recede at rates of the order of 2 A/min. A fraction of the sputtered particles, consisting of both implanted species and target species, is ejected in the ionized state so that by using a specially modified quadrupole mass spectrometer and monitoring the intensity of these secondary ions as the surface recedes, the profile with time of the implanted species can be determined. By calibrating, this can be converted to a depth profile. Results for various ion-target combinations are presented together with an investigation of the effects on ion yield of surface contamination. Also the sensitivity of the ...