Abstract
Wafer topography measurement by using the phase-shifting shadow Moire method has been reported recently. However shadow Moire method is not capable to measure the wafer with a specular surface. In this paper, a wafer topography measurement system with LCD (liquid crystal display) is designed and demonstrated based on four-step phase stepping fringe reflection method using LCD. Wafer bows can be achieved by analyzing the fringe patterns reflected from the specular surface, and film stress can be obtained subsequently by transforming this wafer curvature using a conversion equation such as Stoney's formula. Surface profile of PECVD nitride and oxide coated wafers are measured by a shadow Moire system from the substrate side, and by a fringe reflection system from the coated specular side. A very good agreement between the results obtained from the two methods. Comparing to the result from a commercial profiler, the difference is less than 2μm. This system is especially suitable for stressed films with specular surface. Wafer bow obtained by fringe reflection method is based on full-field information and it would have a better accuracy and better thin film stress characterization
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