Topography based wafer clustering for wafer level overlay correction

摘要

Non-linear overlay deformation is a well-known problem in critical lithography steps. A significant root cause is nonuniform stress, often caused by high temperature processes. Non-uniform stress in the wafer causes vertical deformation of the wafer, which can be measured by topography measurement equipment. In this case study, clustering is done on the topography data to sort each wafer into groups. Using the context information from the clustering, overlay feedback is computed on a wafer level basis. The evaluation of the approach is done with a run-to-run simulation, which allows optimization of this method and evaluation of the on-product overlay performance improvement. In the analysis, different wafer zones are distinguished to characterize the improvement potential for the different zones.