Mechanical stress analysis of an LDD MOSFET structure

This paper presents a mechanical stress study of the LDD MOSFET structure. The stresses are successively evaluated through the forming steps and topological modifications are proposed in order to minimize the residual substrate stress. The analysis is based on a two dimensional finite element method. It includes the cumulative effects from the thermal oxidation, the thermal cycles and the intrinsic stresses, allowing the estimation of the evolution of the stress field during the manufacturing. A nonlinear viscoelastic approach is used to model the nitride, thermal and deposited oxides rheological behaviors. For those oxides, a complete calibration of the mechanical properties is proposed.