In this paper, a new calibration tool for scanning probe microscopes (SPMs) is presented. SPMs are widely used to provide high resolution images of technical surfaces and surface properties. For critical measurement applications, Metrology SPMs with built-in length measurement systems, such as strain gauge or capacitance sensors, are the instruments of choice. Only few Metrology SPMs are equipped with high quality measurement systems that offer easy traceability to national length standards, such as laser interferometers. Every measurement system that is used in precision measurement or quality assurance processes has to be traceably calibrated. This is usually done by step height standards (z) or calibration gratings (x-y plane). Common height standards for SPMs feature one or more fixed steps. The step heights are to be calibrated prior to use by an instrument of higher accuracy, a calibrated SPM. It is not possible to calibrate the full motion of an SPM with such step height standards, they are not flexible enough. Our new tool consists of a stage that is built arund a high precision laser interferometer to ensure easy traceability. The height of the stage can be varied with high accuracy while the SPM probes a flat silicon surface on top of the tool. The tool is small enough to replace a sample in an SPM and thus can be used as a variable step height standard to calibrate the full range motion of an SPM. This paper introduces basic principles, characteristics, and capabilities of the calibration tool.
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