A crystallization and surface evolution study of Au thin film on unpolished Si(100) substrates after annealing at different temperatures above the eutectic point of the Au/Si system are reported. Samples were prepared...
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A crystallization and surface evolution study of Au thin film on unpolished Si(100) substrates after annealing at different temperatures above the eutectic point of the Au/Si system are reported. Samples were prepared by conventional evaporation of gold in high vacuum (10-7mbar) environment on substrates at room temperature. Thermal treatments were performed by both furnace and flame annealing techniques. After evaporation, some Au crystallizes were textured in the (111) direction. However, most of the thin film was amorphous and gold silicides such as Au7Si and Au3Si were also found. This crystallization can be achieved by furnace annealing or flame annealing in spite of the differences between their cell parameters. Annealing overcomes the mismatch between the cell parameters arranging the Au layers in the (111) direction and forming gold islands on the surface. Crystallization of gold strongly depends on both, the temperature and time of annealing. Epitaxial formation of Au can be easily reached after some minutes in the case of flame annealing. The epitaxial temperature for Au/Si(100) should be around the eutectic (363 oC). Above the eutectic point, the Au layer melt, the melting starts most likely from grain boundaries and from the interface allowing the islands separate even further and change shapes until hexagonal geometries. The mean crystallite diameters grow up to a maximum mean size of around 90 nm. The free activation energy for grain boundary migration above the eutectic temperature is 0.09 ev. Therefore the type of the silicon substrate changes the mechanism of diffusion and growth of crystallites during annealing of the Au/Si system.
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