MECHANICAL-STRESS ANALYSIS OF AN LDD MOSFET STRUCTURE

This paper presents a mechanical stress study of the LDD MOSFET struct ure. The stresses are successively evaluated through the forming steps and topological modifications are proposed in order to minimize the r esidual substrate stress. The analysis is based on a two dimensional f inite element method. It includes the cumulative effects from the ther mal oxidation, the thermal cycles and the intrinsic stresses, allowing the estimation of the evolution of the stress field during the manufa cturing. A nonlinear viscoelastic approach is used to model the nitrid e, thermal and deposited oxides rheological behaviors. For those oxide s, a complete calibration of the mechanical properties is proposed.