High-speed metrological large range AFM

Abstract

A high-speed metrological large range AFM (Met. LR-AFM) which is capable of fast, accurate, and large range measurements of surfaces and nanostructures is presented. In its design, the z scanner is realized by combining a piezo stage and a large range mechanical stage (referred to as a nanopositioning and nanomeasuring machine, NMM) which move the sample in parallel, thus providing both a high dynamic positioning capability and a large motion range. A contact mode AFM which offers both a short response time and a large sensing range is applied for measuring the surfaces of interest. Sensor signals from the AFM, the piezo stage, and the NMM are combined to derive the surface topography, thus offering high bandwidth for high-speed measurements. To reduce the distortion in the measured profiles, the time delay of the sensors is corrected as well as the displacements of the AFM and the piezo stage being traceably calibrated referring to the z-interferometer of the NMM in situ. Experimental results have demonstrated the high image quality obtainable at a scan speed of 500 μm s−1. The measurement repeatability at different scan speeds ranging from 10 μm s−1 to 1000 μm s−1 reaches nm for step height measurements and × 10−6 for grating pitch measurements, respectively. The study has improved the measurement speed of the Met. LR-AFM by a factor of more than 20, and thus significantly enhanced its measurement throughput and reduced its measurement drift.