Imaging and illumination system with aspherization and aberration

Abstract

The imaging and illumination system with aspherization and aberration correction by phase steps includes two transparent phase plates within the optical train of a stepper illumination system. The first plate places each ray at the corrected position on the axial stigmatism plate to satisfy the sine condition. The second plate, which is the axial stigmatism plate, ensures that each ray of light focuses at the focal point. The aberration corrected light is reflected by a deformable mirror toward a secondary mirror, a primary mirror and finally onto a wafer to project a single field of large dimension. The secondary and primary mirrors provide aspherization by forming phase steps in the surfaces of the mirrors. The deformable mirror, to permit realtime correction of aberrations and manipulation of the beam for each field imaged by the system. A set of two-dimensional scanning mirrors is placed between the laser light source and a reticle containing to pattern which is to be transferred to the wafer. These mirrors step a beam across the reticle a single sub-field of the pattern at a time. Such individual stepping permits the deformable mirror to correct for each sub-field thereby allowing a very large field of view for the image transferred to the wafer.