Further Improvement of the Measurement Capability of the Metrological Scanning Probe Microscope Veritekt C

摘要

In this paper results of improvement on the metrological scanning probe microscope (SPM) Veritekt C, used at PTB for surface topography calibration purposes, are reported. The Veritekt is equipped with three miniaturised planar homodyne laser interferometers for tracing the measurement result to the meter definition. A high-end DSP-based system has been designed for real-time signal processing and servo control in the instrument. With an embedded Heydemann correction method the inherent nonlinearities of the interferometers can be reduced from 3.5 nm to 0.3 nm in real time. Using multi-channel 16-bit A/D converters the resolution of the interferometers and the demodulation time have been improved, which led to a decrease of the overall measurement uncertainty. Furthermore, a "scan-on-the-fly" measurement mode is realised for higher scanning speed by adopting a highly synchronised data acquisition method. Investigations have shown, that it improves the measurement speed about 10 times.