Dynamic Monte Carlo Simulation of Ion Beam and Plasma Techniques
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DYNAMIC MONTE CARLO SIMULATION OF ION BEAM AND PLASMA TECHNIQUES W.MOLLER Max-Planck-Institut filr Plasmaphysik, EURATOM-Association, W-8046 Garching, Germany
ABSTRACT A multiprojectile version of TRIDYN has been employed to simulate ion-induced effects which occur during ion-beam assisted deposition (IBAD) or plasma-assisted chemical vapour deposition (PECVD) of thin films. Simulations of the formation of boron nitride films deposited from evaporated boron and energetic nitrogen show an excellent agreement with experimental results for nitrogen concentrations below the stoichiometric limit. For high N/B flux ratios, non-collisional mechanisms (ion-induced outdiffusion, surface trapping of outdiffusing nitrogen) have been included in the simulations, again producing good agreement with the experimental results. Simulations of the PECVD of hydrocarbon films suffer from the poor knowledge of the neutral and ionic fluxes which contribute to the growth of the layers. Nevertheless, the composition of the films and its dependence on ion energy can be predicted with satisfactory agreement with experimental findings. A simple model of preferential dis2 3 placement yields a reasonable average ratio of sp and sp coordinated carbon atoms. The energy dependence of the bond ratio is in contradiction to experimental observation. INTRODUCTION Ion irradiation effects are known to play an important role for the growth and properties of thin films being deposited by the assistance of ion beams or plasmas'-5. Although numerous phenomenological studies axe available and some qualitative understanding has been achieved, the quantitative modelling of ion bombardment effects is still at an early stage. Ions may act on a growing film physically through collisional effects like implantation, sputtering, atomic relocation or radiation damage. In addition, ions might promote chemical reactions at the surface or in the bulk, or they might enhance diffusion or precipitation. For the purpose of quantitative modelling, sufficient basic knowledge is only available for the collisional effects. Thereby, first model calculations will apply to systems in which mainly physical mechanisms control the growth rate and determine the film properties. 6 Recently, Carter et al. published an analytical altered layer model for the growth of thin films under the influence of atomic relocation and sputtering. Very simplistic analytical expressions, taking only into account the reflection of the energetic component and the sputtering of the thermal component, have been given by Hubler and VanVechten 7 et al. for the IBAD of nitrides '. The evaluation of the analytical predictions requires data for, e.g., ion reflection or sputtering which are conveniently taken from static binary collision approximation (BCA) computer simulation'. The results of such simulations may alternatively be inserted into rate equations governing the layer growth. Such an 0 approach has been chosen by Muiller' in order to treat the ion-induced densification of oxide films. As a further p
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