Stress relief and hillock formation in thin lead films

The growth of hillocks on Pb films on glass substrates was observed by heating the films inside a scanning electron microscope. Hillocks were found to grow with increasing temperature. The kinetics were such that, at 50°C, the growth was essentially complete in a few minutes. During subsequent cooling, the size of many of the hillocks decreased with decreasing temperature, and cavities formed and grew at the film surface. Analysis of the observations suggests that the stress-relaxation phenomenon which causes hillock growth may be due to grain-boundary sliding and diffusion creep. © 1970 The American Institute of Physics.