Purity and morphology of aluminium films

A continuous wire feed source of aluminium of 99.999% purity in conjunction with a composite ceramic boat has been used to deposit aluminium films of high purity in vacuum. The impurity content was analysed by proton-induced X-ray analysis with a Van de Graaff accelerator, supplemented by X-ray fluorescence, optical emission and Auger electron spectroscopy. The low impurity content achieved (∼ 50 atomic ppm) is attributed to the small quantity of molten aluminium maintained in the boat at one time. The morphology of the Al films was studied by reflection electron diffraction, X-ray diffraction and scanning electron microscopy. Thick Al films grew with {111} and {311} texture orientations. The grain size variation with thickness generally followed the known variation with the deposition rate.