We have investigated step-in mode non-contact atomic force microscopy (NC-AFM) for precise measurement of fine and steep structures having high aspect ratios. We have proposed piconewton controlled step-in mode AFM using NC-AFM to suppress bending and slipping of the probe on a slope. We have constructed a prototype of the step-in mode NC-AFM using a quadrature frequency demodulator for detecting the resonant frequency shift of the cantilever. Experiments revealed that the system was able to perform step-in mode NC-AFM even in air. We obtained a faithful AFM image of the steep structure of a dry-etched Si pattern without bending or slipping of the probe at approximately 2-3 pN using a sharp, slim probe, as compared with a step-in mode contact AFM image obtained at 1, 5, and 10 nN.
We have studied a step-in mode non-contact atomic force microscopy (NC-AFM) for precise measurement of fine and steep structure with nanometer resolution in air. When a high aspect structure is measured using step-in mode AFM with the sharpened and slim probe, it is required that AFM control has to be performed at a force of <1 nN in pico-Newton range to suppress the bending and slipping of the probe on slop. Using a home-made step-in mode NC-AFM using a quadrature frequency demodulator for resonant frequency shift of the cantilever, the NC-AFM demonstrated that Si steep structure was faithfully observed at about 2 pN in air.
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