Auto-correlation of measuring inaccuracies in lithography system - forming superimposed images of linear and strip grids on high resolution film, subjecting to effect for set time, and observing using microscopic

摘要

The method involves illuminating a linear grid with a corpuscular optical beam-system under investigation and using a high resolution recording film. An image of a strip grid of the same grid constant but slightly relatively rotated is superimposed onto the film after a finite period, table movement or other influence on the equipment. The resulting beam position error relative to the first image is magnified in the direction perpendicular to the grid direction by the reciprocal of the rotation angle. It can be directly read off in nanometres from the Moire strips using a microscope after developing the substrate. USE/ADVANTAGE - For quality control of lithographic processes, allowing measurement of position errors, thermal and mechanical instabilities, and image distortion. Accuracy of a few nm is achieved with direct read-out not requiring computer processing.