As geometry sizes decrease and mask sizes increase, the importance of high speed automatic mask inspection is increasingly evident. High speed scanning of large surfaces, while recording the location of artifacts less than 1/10 the size of a hair in less time than it takes to talk about it, presents some formidable problems for the optical architecture of the system.
Kenneth A. Snow,
"Optical Problems Of Small Geometry Automatic Mask Inspection", Proc. SPIE 0135, Developments in Semiconductor Microlithography III, (6 September 1978); doi: 10.1117/12.956118; http://dx.doi.org/10.1117/12.956118