Abstract

The interferometer used in this in situ stress-measurement study was built by Optical Coating Laboratory and is based on a cat's-eye lens.¹ The film stress is derived from the measurement of the evolution of a circular fringe pattern that is produced between the surface of the lens and the back surface of the reflecting substrate. A study of the stress–strain relationship is presented in the case of thin films of aluminum (0.1μm) grown on a thin glass substrate (250μm). The interferometer is positioned inside a low-pressure oven (1 mbar) in order to minimize the combined effects of water desorption and oxidation during heating. The samples are subjected to heat cycles between 20°C and 270°C. Because the thermal coefficient of expansion of glass is smaller than that of aluminum, the film is under compressive stress as the temperature is increased. Experimental results are presented that show that the sample undergoes both a reversible thermal stress and a plastic yield during each temperature cycle.

© 1990 Optical Society of America