The system is suitable for recording and replaying holographic images in real time or storing them for replay later. Similarly, the ability to immediately store the digital data provides a method for digital holographic interferometry. Holograms of the same object, after some physical change such as stress, temperature, micromachining, etc., can be subtracted from one another to calculate a physical measurement of the change in the surface structure. Similarly one object can be compared to a like object to measure the deviations of the second object from the first or master object, by subtracting their respective holograms, e.g., in defect detection applications. Schematic showing comparison analysis used to develop defect masks.
Input can be either the phase or intensity image.
Top row shows processing of intensity data while bottom row shows profile data for the same via region of the wafer. After a pair of images have been obtained, i.e., a reference and test image in either intensity or phase, the test image is registered, or aligned, to the reference. For the purposes of this analysis, and due to the physical alignment inaccuracies of the current stage system, four tie points were selected from the test image and correlated with the reference to correct spatial differences. The grey-scale intensity map of each image was also corrected to reduce intensity offsets between the image pair. The images were then subtracted.