Fabrication and test of piezoresistive cantilever sensors for high-aspect ratio micro metrology

Abstract:
A novel tactile probe based on a cantilever sensor is presented designed for quality assurance of high-aspect ratio micro parts, e.g. complete 3D measurements inside deep and narrow holes, shallow channels etc. It comprises a probing tip at its free end and a low-noise piezoresistive strain gauge at its suspension to avoid the restrictions by the conventional optical read-out of AFM probes. Prototype sensors of lengths of 1.5 to 5 mm, widths of 30 to 200 µm and heights of 25 to 50 µm have been realised using silicon bulk micromachining in a small-scale laboratory process as well as in a CMOS-compatible 4”-wafer-scale production line. Careful calibration of both types of sensors is performed at nanoscale resolution of probing force and tip deflection. Their cross sensitivity to temperature and light as well as their noise and overloading limits are addressed in detail. Sensor performance and tip wear during scanning are investigated at typical probing conditions of tens of muN forces and mm/s speed confirms the potential of the novel cantilever sensors for in-process metrology. Applications of the sensor for shape and roughness metrology with spherical test structures are described.