Measurement of effective source shift using a grating-pinhole mask

Abstract

A methodology for measuring the effective illumination source shift in exposure tools has been established. A grating-pinhole mask is placed upside-down on mask stage, and exposed. This mask consists of square pinholes with 80 micrometers square and 2D square lattices in these pinholes. The pitch of the grating pattern is suitably designed so that the 1st-order diffraction beams can illuminate the edge of the pupil of the projection optics. Both the shape of illumination source and the silhouette of the pupil of the projection optics are projected on the wafer located by normal photoresist. A conventional optical microscope is available for easily observing the photoresist patterns. The grating-pinhole consisting of attenuated phase-shifting structure has found to be also effective to measure both effective coherence factor and intensity non-uniformity of effective illumination source.