Whole field residual stress measurement using computer aided reflection grating

Abstract

In our previous paper, "Warpage of thin wafers using computer aided reflection moire method," the surface curvature and residual stresses were evaluated using the versatility of computer aided reflection grating method to manipulate and generate gratings in two orthogonal directions. A very good agreement between the theory and experimental results was established. The bending stresses of wafers due to the deposition of backside metallization were evaluated without the aid of reference grating. In this paper, some aspects of the work is extended. An optical flat with flatness λ/10 is used as a reference plate to extract the residual stress of the wafers with different backside metallization. By utilizing the phase information from the moiré pattern between deformed grating (wafer) and undeformed grating (optical flat), the surface deformation of the wafer and residual stresses are investigated quantitatively and numerically. This technique, with satisfactory sensitivity and accuracy, can be used to characterize the residual stress of wafer due to warpage that may lead to the crack issues in semiconductor manufacturing industry.