Abstract

The scattering matrix approach to computing the image of a multilayered structure¹ is used to study alignment mark-induced offsets in microlithography. The sensitivity of the offset to different types of illumination and imaging system, to misalignments in the illumination and imaging optics, and to different alignment mark structures is presented. In particular, reverse dark-field imaging is studied in detail. The effects of nontelecentricity and coma for several alignment mark shapes are presented. The offsets are shown to be particularly sensitive to alignment mark shape and to layer thickness as well as aberrations. To obtain offsets that are less than a tenth of a micron with a given range of aberration and misalignment in the optics requires the use of particular alignment mark shapes or the use of a more sophisticated algorithm for determining the mark position from the image. The basis of the scattering matrix approach to imaging layered media is briefly discussed for the purposes of understanding the results of the model.

© 1988 Optical Society of America