Detection of the displacement of micro touch probes using structured illumination

To decrease the effort to detect micromechanical features by touch probe measuring systems, multiple touch probes composed in an array are used to measure some of these structures at the same time, owing to the alignment of many similar structures on a wafer. While in previous works the touch probe signal is read out electrically, using optical techniques by observing the reflective back plane of the micro probe array is a promising approach to detect the displacement of several touch probes simultaneously. In this investigation a structured illumination measurement system is used to detect the deflection of the micro touch probes. By detecting several fringe patterns with different periods, orientations, and phase-shifts a correlation between the coordinate of a CCD camera pixel and the observed monitor pixel coordinate can be obtained. A deflection of the touch probe leads to a deformation of the reflective back plane of the micro probe array and, thus, a different monitor pixel coordinate is observed by the CCD pixel. Using an image obtained with an undeformed touch probe array as a reference, the displacement of the touch probe can be derived.