Abstract

The principle of operation of the modulated transmission elipsometer (MTE) stress measurement technique and some specific thin film and bulk material systems that have been studied using the MTE are discussed. The MTE is an optical setup that uses a highly sensitive polarization modulation technique and an x-y galvanometer scanner for high speed mapping of internal stress birefringence in transparent optical materials. The MTE can measure stress generated retardances of the order of 0.01-160 nm in areas of from 50 × 50 μm to 100 × 100 mm. This system also has the unique ability to recognize and actively subtract optical component stress by imparting a controlled retardance bias on the laser beam. The output can be displayed as a line scan, 3-D plot, or a color contour plot. The MTE has been used to observe internal stress in dielectric thin film/substrate systems such as Cu, Ta₂O₅, and Si, in various transparent substrate materials. Thin film multilayers of MgF₂ and ZnS on BK-7 substrates have been examined for stress as a function of predeposition and postdeposition parameters. The effects of stress on transparent Cu thin films on a glass substrate were studied by repeatedly stress mapping the system for varying levels of current through the Cu. Stress research has also been done on bulk materials such as strengthened glass, polymers, Nd:doped laser glass, and electrooptic crystals. The MTE has allowed us to compile a continually growing data base on the causes and effects of internal stress in thin film and bulk materials.

© 1989 Optical Society of America