Molecular Dynamics Simulation Of Thin Film Growth In The Initial Stage

Recently, the growth process of thin film has been directly observed in experiment with developing of the surface detection technology for many materials. Using scanning tunnel microscopy (STM) and atom force microscope (AFM), one can observed island structures of thin film, surface reconstruction and adatoms diffusion, especially the migration of the individual embedded Ge atoms within the Si(100) surface. However, many physical processes (for example, deposition, diffusion and combination, etc.) on the substrate surface for many species of particles (single particle, cluster, vacancy, step and dislocation, etc.), which are particularly important during film growth in the early stage, are still limited in experimentation and etection technology. Therefore, it is necessary to investigate the interaction between deposition particles and substrate atoms in the atomic scale, and microscopic details involved and microstructure evolution during the initial stages of film growth. Understanding the microstructure evolution of the films growth (including surface morphology, microstructure, componental content and distribution) could improve technological processes and manufacturing conditions, and further save the production cost of thin flim. This is particularly important to enhance film properties and promote the development of the relevant industries.In our works, transport behaviors of the deposition atoms, growth evolution of the submonolayer film and the influences of thermal annealing on the film growth process for Cu-film on Cu(001) substrate are investigated by molecular dynamics (MD) simulation. Here, the embedded atom method (EAM) potential is used to describe the Cu-Cu many-body interactions.In the research of deposition and transport behaviors of the individual atoms onto the substrate surface, it is concluded that transport behaviors of the deposited Cu atom with 1-30 eV onto Cu(001) surface are closely related to both the local impact site and the incident energy. The observed transport behaviors of the deposited atom include:direct adsorption (DA), penetration by atomic exchange, and transient penetration (TP), which a deposited atom penetrates the interstitial site and then rapidly migrates to a stable site on the surface. Furthermore, when the incident energy is higher than the penetration threshold, TP behavior could be observed again in some energy ranges. This interesting phenomenon, which can not be explained by the existing theories, is possibly attributed to the dynamical competition between the deposited atom and substrate atoms.For the study of the influence of thermal annealing on the submonolayer Cu-film, one could find that the submonolayer film has a tendency to grow in layer-by-layer mode at the substrate temperature of 300-500 K and incident energy of 1-5 eV. The atomic mixing on the substrate surface occurs when increasing the incident energy and/or the substrate temperature. However, deeper and more penetration on the surface is not observed after annealing treatment of the submonolayer film. Before annealing, the surface roughness decreases with increasing the incident energy and reaches the minimum near a certain optimal substrate temperature. By annealing at 600 K, however, the surface roughness significantly decreases and the maximum residual stress in the top layer of the film is remarkably released simultaneously with unchanging the layer structure of the film.The growth conditions and the annealing temperature of the multilayer film in MD simulation are the same as that of the submonolayer film. The results indicate that the multilayer film grows in the layer plus island mode. The surface morphology and roughness evolutions of the films before and after annealing are similar to that of the submonolayer film. The film surface becomes smoother and its microstructure is ordered after thermal annealing. Furthermore, layer coverage and radial distribution function (RDF) are associated with the incident energy and substrate temperature. The peak values of RDF are increased after annealing, and this indicates that annealing treatment could enhance crystallization of thin film. In addition, the maximum normal force and stress in the top layer of the film are decreased by thermal annealing. Therefore, the high quality flim with dense structure could be obtained by thermal annealing at appropriate growth conditions.