Development of a tunnelling current sensor for a long-range nano-positioning device

Abstract

Dimensional micro and nano metrology is gaining enormously in importance with the development and advancement of micro mechanics (e.g., micro gears), micro electronic and mechanical devices (e.g., MEMS, miniaturized sensors), micro optics (e.g., cameras in mobile phones) and nanotechnology (e.g., functional surface layers), but effective and efficient quality control in these fields is hindered today by the lack of powerful, flexible, robust and economic tools for nanometre-resolved 3D metrology. Scanning probe microscopy (e.g., AFM) suffers from small measuring ranges, fragility, a lack of flexibility and usually unsatisfactory metrological properties such as repeatability and linearity. Miniaturized tactile 3D coordinate measuring machines (CMMs) today only deliver very low point rates and are not suitable for measuring surface fine structure due to the characteristics of their probing elements and their dynamic properties. Additionally AFM tips tend to wear and micro CMMs may damage the workpiece. To overcome these limitations a laser-interferometrically controlled 3D nano- positioning and measuring machine (NMM-1) with a measurement range of 25 mm × 25 mm × 5 mm and sub-nanometre positioning resolution has been equipped with a custom made current measuring probing system. The use of electrical probing interaction in the nanoampere order instead of force (tactile probing, AFM) gives much more flexibility for size and shape of the probing element, as gravitational influence and stresses in the probe are not relevant for probing performance. The combined system can be used as a metrological long-range scanning tunnelling microscope, but also as a 3D micro CMM and provides nanometre resolution combined with an outstandingly large measuring range of several millimetres and traceable position measurement via three helium–neon (HeNe) laser interferometers. Results of the experimental set-up show that the combination of laser interferometry and electrical probing can deliver a reproducibility of down to 3 nm at ranges of several millimetres.