Using the technique described in part I, the energy spectrum of sputtered atoms has been determined for several gold specimens, both single crystals and polycrystalline aggregates. The ⟨110⟩, ⟨110⟩ and ⟨121⟩ directions of ejection were chosen for the experiments. Bombardment was with either 43 kev A+ ions, 43 kev Xe+ ions or 66 kev Xe+ ions. The energies of the ejected atoms ranged from some 10−2 ev up to about 104 ev. A peak was generally observed in the energy spectrum between 1 and 10 ev. On the high energy side of this peak the spectrum behaved roughly like E −2, though there were significant deviations from this, particularly for ⟨100⟩ ejection. A theoretical model is developed in which ejection results principally from the generation of atomic collision cascades by the bombarding ion. The assumptions that energy in the cascades is shared by two-body collisions and that the mean collision free path is independent of energy lead to an E −2 spectrum and this prediction should hold roughly from...

II. The energy spectrum of ejected atoms during the high energy sputtering of gold

The Monte Carlo Program TRIM.SP (sputtering version of TRIM) was used to determine sputtering yields and energy and angular distributions of sputtered particles in physical (collisional) sputtering processes. The output is set up to distinguish between the contributions of primary and secondary knock-on atoms as caused by in- and outgoing incident ions, in order to get a better understanding of the sputtering mechanisms and to check on previous theoretical models. The influence of the interatomic potential and the inelastic energy loss model as well as the surface binding energy on the sputtering yield is investigated. Further results are sputtering yields versus incident energy and angle as well as total angular distributions of sputtered particles and energy distributions in specific solid angles for non-normal incidence. The calculated data are compared with experimental results as far as possible. From this comparison it turns out that the TRIM.SP is able to reproduce experimental results even in very special details of angular and energy distributions.

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Sputtering Studies with the Monte Carlo Program TRIM.SP

The extent to which gas‐surface chemical reactions can be enhanced by energetic radiation (primarily ions and electrons) incident on the surface is described. Emphasis is placed on chemical systems which lead to volatile reaction products. In particular, the reactions of Si, SiO2, and Si3N4 with XeF2, F2, and Cl2 are examined experimentally. Possible mechanisms for the radiation‐induced enhancement are discussed and some technological implications of this process in plasma etching technology and lithography are considered.

Ion- and electron-assisted gas-surface chemistry—An important effect in plasma etching

Based on the sputtering version of the TRIM program for multicomponent targets, a Monte Carlo code has been developed which computes range profiles of implanted ions, composition profiles of the target and sputtering rates for a dynamically varying target composition. It takes into account compositional changes both due to the spatial distribution of target atoms deposited in collision cascades, and due to the presence of the implanted ions. The local density of the target is allowed to relax according to a given function of the densities of the individual components. The applications of the program cover a wide range of problems like the collisional atomic mixing of multilayered targets, dynamic implantation profiles at large fluences, and the fluence-dependent preferential sputtering of multicomponent materials. The present paper provides a description of the program and a critical comparison to similar Monte Carlo codes. As an application, the behaviour of the Ta-C system under He bombardment is studied with respect to sputtering yields, surface composition and composition profiles. Satisfactory agreement is obtained with experimental results given in the literature.

Tridyn — A TRIM simulation code including dynamic composition changes

Low-energy ion scattering at surfaces

Low energy ion impact phenomena on single crystal surfaces

This article has two primary objectives: to present a status report on our present understanding of the physics of atom ejection by ion bombardment and to indicate the contributions of molecular dynamics simulations to this research area. Because this application of molecular dynamics is relatively unfamiliar, basic simulation techniques useful in open systems are described in some detail. While this review discusses the current situation, explanations and historical background are necessarily included to place problems in perspective.

Application of molecular dynamics simulations to the study of ion-bombarded metal surfaces

Molecular-dynamics simulations have been performed for the keV particle bombardment of Si{110} and Si{100} using a many-body potential developed by Tersoff. Energy and angle distributions are presented along with an analysis of the important ejection mechanisms. We have developed a computer logic that only integrates the equations of motion of the atoms that are struck, thus decreasing the computer time by a factor of 3 from a complete molecular-dynamics simulation.

keV particle bombardment of semiconductors: A molecular-dynamics simulation.

This article surveys the present state of sputtering theories. Similarities and differences between the statistical theories and atom ejection simulations are discussed in detail. The limitations of both approaches are considered, and the different viewpoints are contrasted. Some computer simulation model results for atom ejection from pure metal single crystals are summarized. The implications of these results, and their contribution toward the future development of sputtering theory is indicated.

Sputtering models—A synoptic view

The mechanism for the formation of small metal clusters ejected from an ion bombarded metal surface is examined in detail. The analysis is performed by classical trajectory methods which determine the positions and momenta of all particles in a model microcrystallite as a function of time. The calculation utilizes pair potentials for Cu derived from elastic constants of the solid and is performed for 600 eV Ar+ ion at normal incidence to the crystal. The results show that cluster species do not leave the surface as intact parts of the solid but form in a region above the surface. A trajectory for Cu5 formation is traced in detail showing a typical mechanism which is valid for Cun formation where n?7.

Don E. Harrison

Papers

Low energy ion impact phenomena on single crystal surfaces

Application of molecular dynamics simulations to the study of ion-bombarded metal surfaces

keV particle bombardment of semiconductors: A molecular-dynamics simulation.

Sputtering models—A synoptic view

Formation of small metal clusters by ion bombardment of single crystal surfaces