Investigation of the metrological properties of a 3-D microprobe with optical detection system

Dimensional measurements of microstructures with uncertainties below 50nm require both nanopositioning and nanomeasuring machines (NPMMs) as well as appropriate microprobes. This paper introduces a novel 3-D tactile microprobe system developed at the Ilmenau University of Technology, Institute of Process Measurement and Sensor Technology, and contains an analysis of its metrological characteristics. This microprobe system uses a silicon membrane to induce the measurement force and to operate as the damping system for the stylus. This damping is entirely brought about by internal friction. An optical detection system measures the deflection of the membrane and thus of the stylus. The optical detection system uses a single laser beam, focused on the backside of the silicon membrane. The reflected beam is split, with one part being used to measure the tilt about the x- and y-axes and the other part being fed back into an interferometer for deflection measurement in the z-direction. Thus, the deflection of the membrane can be measured with sub-nanometre resolution. An NPMM was used to analyse the metrological characteristics of the microprobe system and to calibrate it. This paper focuses on a detailed analysis of the three-dimensional reproducibility for point measurements by obtaining and evaluating a directional response pattern. This pattern is then compared to the behaviour of other microprobe systems. Furthermore, the work shows that the microprobe system can be applied successfully to scanning measurements and satisfactory results obtained. These results indicate that the microprobe system is well-suited for universal measurement tasks in dimensional metrology.