Implementation of New Robustness Assessment Methodology for Crack Stop Constructions

The paper describes an automated optical inspection method by using the new dedicated binning approach. The procedure is used as new robustness assessment methodology for crack stops. The effectiveness of crack stop design components was characterized and crack lengths were determined. Correlation of experimental and simulation results will be presented. Crack stops are used in semiconductor chip designs to avoid crack propagation towards active chip area after die separation. The knowledge of the robustness of these crack stop constructions is the key factor for the improvement of these designs and to master increasing complex material stacks. The described robustness assessment methods for crack stops allows to evaluate different components individually, which is not the case by using typical approaches. The new optical robustness assessment methodology uses the standard automated optical inspection (AOI) tool with the new developed dedicated binning approach (DBA). The DBA can be used to estimate the effectiveness of each design component of the crack stop construction. In the paper, experimental results of the robustness assessment of different crack stop constructions with different components by using the new method will be presented. Based on DBA, the effectiveness of each design component is individually assessed. A determined yield loss after separation by using AOI with DBA was introduced as a selection criterion for the most robust crack stop variant. The quality of the detectability of chipping and delamination defects by AOI was confirmed by dark field optical inspection. For the most robust variants (identified by using AOI-DBA), Finite Element numerical simulations were used to investigate their plastic deformation behavior with respect to crack propagation inside the crack stop components. The result of the numerical simulations, which correlates to Focused Ion Beam analyses (FIB) of these structures, will be shown. By using the AOI-DBA method, the robustness of several crack stop variants can be compared directly. The output of AOI-DBA can be used as an input for parameterization of models for Finite Element simulation. Based on this, a cost saving can be ensured because the design optimization can be done in the early stage of technology development without usage of silicon hardware. Moreover, silicon area can be potentially saved and a higher robustness can be gained.