Miniature silicon Michelson interferometer characterization for dimensional metrology

Dimensional metrology applications require performing measurements of profile and form/shape of parts at a nanometer-level of accuracy. Therefore, the metrological characteristics of a miniature optical micro-probe based on a Michelson interferometer are evaluated. The optical micro-probe is designed to perform dimensional measurements with a target uncertainty in the order of few nanometers. Two micro-probe designs having reflection-transmission ratios of 75-25% and 25-75%, are characterized. Two optical setups have been implemented as well: firstly, using a single laser diode with a 1550.3 nm wavelength and secondly using a tunable laser source in the C-L bands. The characterization of the two micro-probes is performed using a new ultra-precise test bench, with respect to both dissociated metrology structure and Abbe principles. The experiments allow the evaluation of the error sources such as: stability, axial motion errors (residual errors), material dependence, tilt angle and roughness of the tested object. The experimental results revealed that dimensional measurements could be achieved with nanometer-scale errors, ranging from 2 nm to 15 nm, depending on the probe design and the reflectance of the device under test.