Askraba, Sreten (1999) A new vibrational technique for measurement of stress variations in thin films. PhD thesis, Victoria University of Technology.

Abstract

A survey of thin films deposited by standard techniques (electrodeposition, chemical deposition, sputtering, physical deposition, etc.) shows that internal stress is a common problem, particularly in industrial applications. The presence of stress influences the properties of the film and when severe may cause the film to buckle or crack. There is a significant technological and industrial interest in measurements that determine the magnitude of the internal stress. Stress measurement represents a highly sensitive tool for the study of thin film structure in a non-destructive manner. Accurate measurements of the intemal stress in thin films is rather difficult and a number of methods have been described in the literature. This thesis describes a simple all-optical technique for measurement of internal stress in thin films deposited in a vacuum system. The technique is based on a measurement of changes in the modal resonant vibrational frequencies of the substrate/film structure which are caused by stress-induced changes in curvature. The modal vibrations are induced by photothermoelastic bending produced using low-power modulated laser diode light. The vibrational resonant frequency changes are monitored by a sensitive fibre optic interferometer system. A feedback system can allow direct readout of stress-related frequency variations with time as films are deposited or modified by processes such as exposure to the atmosphere. The technique was tested using chromium and magnesium fluoride thin films deposited on glass substrates.

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