Structure end foreshortening: Lithography driven design limitations

Especially in logic lithography, the issue of end foreshortening becomes more and more relevant with increasingly small dimension of the printed patterns. This study examines the effect of illumination condition, mask type, and various feature types on space end foreshortening at 150nm ground rules. Special emphasis is put on end foreshortening induced design limitations, which may prevent linear shrinks. Data from aerial image simulations, and from experimental data on specially designed test masks suggest that especially the variation of the end foreshortening as a function of defocus has to be considered. The most critical geometry is that of nested and butting space ends at minimum groundrules, where the foreshortening cannot be compensated completely by OPC.