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Sub-resonant tapping atomic force microscopy enables topography measurements with limited lateral tip-sample forces, while overcoming the limitations of excessive damage and measurement errors that occur during amplitude modulated operation on high aspect ratio samples. Therefore, it is a candidate to enable process quality monitoring in semiconductor device fabrication. However, at steep edges of such device geometries, the technique often results in stick-slip events for the probe, preventing the desired quasi-static motion of the cantilever and causing errors in the measured topography. To understand the stick-slip dynamics, a model is presented in this article that accurately predicts the consequences of stick-slip episodes. Employing this model, a time-domain based reconstruction technique is proposed to obtain an enhanced topography image. The proposed technique has been tested on a commercially available atomic force microscope with high aspect ratio tip probe and is shown to allow extraction of the topography of a grating sample with overhang features. Comparison of this technique with a conventional AFM method shows improved profile accuracy. |
