Resolution Limit for Two-Dimensional Crossed-Grating Patterns Projected by a Coherent Beam

The resolution limit for two-dimensional crossed-grating patterns created by projecting mask objects by using a coherent beam has been investigated. We consider first two conventional mask types, a binary-amplitude mask and a two-level phase-shifting mask, in analyzing relationships between a diffraction-beam configuration and an image-intensity distribution. Then we derive, as a mask that overcomes the resolution limit of the conventional ones, a four-level phase-shifting structure with which the minimum image period can be reduced to (radikal)2 /2 times that of the two-level phase-shifting mask.