Working Group 5.11

Nanoforce Metrology for Tactile Sensors

3D Micro Measuring Device

The increased industrial use of microsystems gives rise to novel requirements  for quality assurance and for the associated instruments technology. To carry out these dimensional measurement tasks with the uncertainty of measurement required, a 3D micro measuring device (3D-MME) is being developed at the PTB, which allows coordinate measurements on microstructures to be carried out with an uncertainty <100 nm. The range of measurement is 25 mm x 40 mm x 25 mm. The 3D-MME is based on a coordinate measuring machine (CMM) which is available on the market and whose accuracy is increased as high-resolution scales (10 nm resolution) and improved air bearings are used. The basic unit is supplemented by a measuring system to determine the relative position and location of measurement object and measuring system during measurement and to correct the tracing coordinates. The uncertainty contributions due to guiding deviations of the CMM can thus be minimized.

The 3D-MME is equipped with two z-spindles which can be controlled independent of each other. One spindle has an optical coordinate measuring system which, together with a fibre sensor, allows tactile measurements. The fibre probe was developed at the PTB and is available on the market. The second spindle is provided with measuring 3D microprobes which are developed at the PTB in cooperation with the Institute for Microtechnique of Braunschweig Technical University and Carl Zeiss. These are now commercially available on the market.
The flatness deviations of an optical flat were measured with the 2d fibre probe on the 3d micro measuring device. Repeated measurements of flatness resulted in a mean value of 165 nm with a standard deviation of 51 nm. Taking the twofold standard deviation as a measure for the repeatability of the system a value of 100 nm is achieved. The measured mean flatness of 165 nm is a measure for the probing uncertainty of the 3d micro measuring device with metrology frame and fibre probe.
The expanded measurement uncertainty of the 3d micro measuring device with fibre probe amounts for flatness measurements to 236 nm. Main uncertainty source is thermal drift. Without thermal drift the expanded measurement uncertainty of the 3d micro measuring device with 2d fibre probe amounts to 61 nm.