Microstructural studies of the growth of aluminum films with water contamination

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Abstract
Al films were grown at three different water partial pressures. The structure of the films at various thicknesses was observed with transmission electron microscopy. It was found that all three cases grew initially by island formation. (i) At greater thicknesses the film grown at the lowest pressure has large grains and a uniform thickness. (ii) The medium contaminated film has relatively clean regions with large grains and heavily contaminated regions with small grains. Furthermore, the film is not uniform in thickness; the clean regions are much thicker than the contaminated ones. Contamination of Al nucleates at discontinuous regions. Starting at the boundary Al substrate vacuum the contamination extends up to the Al surface. The contaminant layer prevents coalescence and recrystallization of Al, explaining the small grain size in certain areas. (iii) The heavily contaminated film has small grains and a uniform thickness. It is observed that at relatively small thicknesses (50 nm) the Al surface is already contaminated, preventing the growth of large grains.