X-ray nanodiffraction analysis of residual stresses in polysilicon electrodes of vertical power transistors

Abstract

The influence of residual stress concentrations on the mechanical stability and functional properties of vertical power transistors is not fully understood. In this work, residual stresses are analyzed in two polycrystalline Si electrodes using synchrotron X-ray nanodiffraction and finite element (FE) modeling. Diffraction scanning was performed over 42 transistors with a step size of 100 nm and the data were subsequently averaged in order to compensate for relatively poor diffraction statistics. The experiment revealed compressive in-plane and out-of-plane stresses of -185 to -225 MPa and -65 to -95 MPa, respectively, in the lower electrode and equiaxial tensile stresses of 70 to 150 MPa in the upper electrode, which appear to be dependent on doping and increase proportionally from compressive to tensile with the electrodes’ dimensions and grain size. The results are interpreted in terms of processing route and correlated with the FE simulation. The comparison shows overall good agreement for in-plane and out-of-plane residual stresses but indicates a limitation of the FE stress simulation regarding the impact of doping and grain size effects.