Impact of filtering on nanotopography measurement of 300mm silicon wafers

The term nanotopography (NT) is used in semiconductor industry for the non-planar flatness deviation of a silicon wafer front-surface within the spatial wavelength range from about 0.2 to 20 mm. Therefore, long-wavelength contributions to a wafer height map are eliminated by high-pass filtering when extracting the NT. The settings of this filter used for NT measurement evaluation may significantly influence the results reported. Height maps of wafers of different NT conditions recorded with an interferometric tool are processed with different filter settings in an experiment with factorial design in order to assess their influence and range of variation. Filter type, filter cut-off wavelength, data extrapolation at the wafer edge, NT metric, and area threshold are varied at two levels each. Filter type, cut-off wavelength, and data extrapolation turn out to significantly affect NT measurement results. These three factors also are subject to strong interactions. Wafers with excellent NT show little dependence on filtering scheme. A double Gaussian filter with constant 20 mm cut-off wavelength appears to be preferable for providing accurate NT height maps. Application of Deviation metric for threshold height analysis allows the correct localization of peaks and valleys in the map and determining "defective" areas on a wafer. (C) 2003 Elsevier Science Ltd. All rights reserved.