Slip band distribution in rapid thermally annealed silicon wafers

Abstract

X-ray diffraction imaging of 200 mm diameter (100) oriented double-side polished silicon wafers has revealed that the slip band distribution, following rapid thermal annealing (RTA), has a lower symmetry than predicted from the material crystallography. Finite element (FE) modelling of the thermal processes has been undertaken and it is found that, in order to predict the measured temperature distribution during the annealing sequence in a commercial RTA furnace, an anisotropic heat flux distribution in the furnace must be included. When such an anisotropic heat flux is used to predict the wafer temperature, it is found that the temperature gradients are not equivalent in the radial direction. Calculation of the resolved shear stresses on the five independent slip systems associated with these gradients predicts asymmetry between the stress on slip bands that project into the [011] and [01¯1] directions. The anisotropy of the resolved shear stress distribution predicts accurately the asymmetry of the experimentally observed slip band length and density. Rotation of the wafer with respect to the furnace axes results in characteristic and systematic changes in the symmetry of the distribution, which is in good agreement with the finite element predictions.