Structure of Al-Hf Films
The structure of Al-Hf thin films, before and after annealing, has been studied by transmission electron microscopy. A 7000-Å layer of aluminum was evaporated, at a pressure of 5 x 10-7 Torr, onto a silicon wafer that had 5000 Å of thermal SiO2 on top. Onto the aluminum layer, with no break in the vacuum, a 1700-Å. layer of hafnium and then a 1000-Å layer of aluminum were deposited. The resulting three-layer structure was used to determine how different atomic ratios of Al and Hf influence the phases formed.After 4 hr of annealing at 400 C in a dry nitrogen atmosphere, the upper part of the film was found to be composed of grains of Al3Hf (ZrAl3-type), about 700 Å in diameter (Fig. 1). The reaction appeared to be complete in the upper layer; none of the relatively large Al grains, 2000 Å in diameter, that had been present in the as-deposited sample were found.