Novel 3D piezoresistive silicon force sensor for dimensional metrology of micro components

This paper reports the successful fabrication and characterization of a novel three-axial silicon force sensor based on piezoresistive transducers and its application in dimensional metrology. The innovative sensor design enables a distinct reduction of the critical ratio S_z /S_x of out-of-plane stiffness S_z to in-plane stiffness S_x. In contrast to existing single-chip sensors with S_z/S_x = 30 a ratio of 4 is achieved which improves the detection of inclined surfaces. The sensor consists of a flexible cross-structure realized by deep reactive ion etching. The arms of the cross-structure are connected to a silicon frame and to the central part of the cross-structure through silicon membranes hinges. A stylus with a probing sphere is used as the tactile element. Forces applied to the sphere are transferred into a deflection of the cross-structure. The respective stress values in the membranes are detected using implanted piezoresistors. The sensor element is applied in dimensional metrology of micro components with lateral dimensions larger than 100 mum. The lateral resolution of the sensor element is 10 nm