Study of the thermal behaviour of thin aluminium alloy films

Abstract

Stress-induced grain and hillock growth occuring in aluminium thin films thermally treated on their SiO2/Si substrates has been studied by in situ transmission electron microscopy (in planar and cross-section geometry) and by electron microscope surface techniques. The mechanical stress has been measured by a cantilever method. The grains, having a (111) texture after their deposition, have been observed to grow preferentially in the direction normal to the film surface. The grain size depends on the temperature-time regime applied: at temperatures higher than 400 °C, enhancing the temperature in a stepwise mode results in grains larger than after isothermal heating. This is attributed to different contributions of the main processes of stress relaxation involved. In the stepwise mode it is grain boundary diffusion that should prevail, whereas in the isothermal mode it is dislocation glide. Two processes of grain boundary movement can be distinguished: a stepwise shift and an instantaneous coalescence. The hillocks are formed in the range between 130 and 300 °C. Their growth is attributed to stress-induced grain boundary diffusion.