Investigation of a fitting phase-shift method for stress analysis using infrared photoelasticity

Abstract

The acquisition of phase information is critical in the infrared photoelastic method. As silicon-based semiconductor devices become increasingly finer, the demand is rapidly increasing for a phase information deterimination method with a high stress resolution. This work proposes a fitting phase-shift method based on the multistep phase-shift method, which is more applicable to samples with small stress states or low stress-optic coefficients. The solutions of the phase difference and isoclinic angle can be extracted from a sequence of in situ photoelastic images by iteratively fitting the intensity values under a series of combinations of optical parameters. This method was further implemented in a four-point bending experiment with silicon. The phase information and stress distribution results were analysed and compared with those obtained by the six-step phase-shift method, showing that the fitting phase-shift method is reliable and has higher precision. A three-point bending experiment was also carried out to verify the accuracy of the proposed method under a complex stress state.