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/sub z//S/sub x/ of out-of-plane stiffness S/sub z/ to in-plane stiffness S/sub x/. In contrast to existing single-chip sensors with S/sub z//S/sub 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 /spl mu/m. The lateral resolution of the sensor element is 10 nm.