Novel test structures for stress diagnosis in micromechanics

Abstract

A novel set of microstructures for on-wafer stress measurement is presented, based on a lancet principle, with dedicated design for the amplification of the dimensional variations induced by the internal stress of the structural material. A tilted arm geometry was adopted in order to maximize the strain induced movement, keeping the design relatively simple and robust and the lancet on the wafer plane. A set of simulations, as well as an analytical examination of the structure was performed to establish the optimal geometry: different tilt angles were simulated in a range between −200 and 200 MPa internal stress. Test structures were then realized by means of surface micromachining, adopting photoresist as sacrificial layer and electroplated gold as structural layer: the novel geometry was sided by traditional rotating structures [Sens. Actuators A 37/38 (1993) 756] and wafer curvature measurements to confirm the readout. Plastic regime simulations were adopted to analyze the behavior of the gold structures, based on a stress–strain curve obtained experimentally.