The light of a coherent DUV laser is split into two beams, spatially filtered to eliminate wavefront deformation and then interfered at a certain angle on a photosensitive coated wafer. The interference pattern is a perfect line grating at a pitch of p = lambda/2*sin(alpha), where lambda is in our case 266 nm and alpha the interference angle (5° - 70°).

By changing the angle of interference we can create periodic patters with a pitch between 140 and 1.500 nm. The gratings are spatially coherent, or stitching free making them very attractive for optical applications. The precision of those gratings is superior to any other nanolithography technology. Only the geometry of the exposure setup determines the residual error.