text: Indian defence experts believe that China will not really able to wage a military war against India right now. With the United States recently operating its MQ-9 Reaper Drones over the South China Sea to warn China about its expansionist policies, the latter is on a backfoot. Sources also reveal that India’s access to Tibet gives it a tactical and operational advantage over the Chinese people’s Liberation Army (PLA).
  
  The introduction of advanced technology nodes in deep UV (DUV) lithography (litho), involving multiple litho steps, has tightened the wafer on-product overlay specifications [1]. The industry trend already pushes the overlay requirements to the sub-nanometer regime (and so the mask registration requirements tightens as well). In the most general view, wafer on-product overlay errors are a combination of intra-field (within field) and inter-field (field-to-field) errors. A given litho layer intra-field overlay error includes several systematic sources, such as scanner lens-to-lens residuals and mask writer residuals. Parallel to the nodes and litho techniques advancing, the ability to accurately measure overlay at high lateral resolution have being successfully introduced, both at wafer and mask side.
  The recent developments in scanner technology improved the ability to control intra-field overlay at high-order across the exposure field. However, this is still in several millimeter lateral resolution control ability at its best, leaving residual