Computer Simulation of the Control of Electroplating

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In this work, the surface structure of thin film deposited on a metal surface, the formation of defects within the film and the control of the surface growth have been studied using computer simulation methods. As a model of solution growth, we extended a basic Solid-on-Solid (SOS) model so that vacancies are created in the film during the growth and performed Monte Carlo simulations for a two-dimensional square lattice. Following results are obtained.1. The surface changes from a layer structure to a rough structure and the density of defects increases as the chemical potential (overpotential in electrodeposition) becomes large. For large overpotential, the nucleation occurs everywhere on the surface and the surface has a fine structure. These results correspond to experimental findings.2. Point defects (single vacancies) appear in the film when the surface has a layer structure. When the surface becomes rough, large voids are formed as well as point defects. The vacancies are created when hollow parts of the surface are filled with deposited atoms. The history of the surface growth is reflected in the void structure.3. When the surface has vias, voids are created and aligned in the direction of the growth. This will produce a pinhole in the film, resulting in the decrease in the corrosion resistance. Voids are also formed when the initial surface has trenches, corresponding to experimental copper deposition for interconnects.4. The simulations of heat treatment are also performed. The surface diffusion is enhanced when the temperature is high, and the roughness of the surface decreases.We also studied the mixing of two liquids (chaos mixing), and developed efficient Monte Carlo simulation algorithm by applying an importance sampling method.