Influence of additional rotational movements on the measurement uncertainty of nanomeasuring, nanopositioning and nanofabrication machines

The measurement of freeform surfaces, aspheric lenses or the sidewall roughness of high aspect ratio structures are a current challenge in nanometrology. There are different publications and commercial products with approaches to perform a measurement of those quantities. Beside the nanomeasurement the nanofabrication on curved freeform surfaces is an upcoming trend. The measurement or the fabrication on a freeform surface is limited by the possible tilt angle between the tools working axis and the local surface normal. To achieve larger angles and a minimal measurement uncertainty the tool must be placed optimal to the local surface. According to those requirements, concepts are developed to increase the degree of freedom in positioning. The x-y-z translational positioning system of an nanomeasuring machine (NMM-1) with a working volume of 25 x 25 x 5 mm3 will be extended by additional rotational movements. The rotation can be achieved by three basic principles of motion which are the rotation of the sample, of the tool or a combination of the tool and the sample rotation. In a first step the principles of motion are described by their bare geometrical properties and decoupled from real positioning systems. A constant instantaneous centre of motion in the sensor measurement point is determined as the optimal principle for a rotational system. This principle is further investigated and is made concrete by choosing a combination of kinematics. A vectorial approach based on the GUM is used to evaluate the influence of the axes error motion on the measurement result. The method and the results for a combination of a rotary table and a goniometer axis are described in detail.