ADAPTIVE OPTIC WAFER STEPPER ILLUMINATION SYSTEM

摘要

The illumination system for a semiconductor wafer stepper includes reflective elements within the projection optics of a primary mirror (10), a secondary mirror (8), a deformable mirror (6) and a beamsplitter (4). The beamsplitter directs light reflected from the wafer surface (24) back into an interferometer camera to provide depth of focus and aberration information to a computer (16) which activates and selectively deforms the deformable mirror (6). Light, input from a mercury arc lamp or laser source, is projected either with an expanded or scanned beam through a reticle (20) which is printed with the pattern to be transferred to the wafer. An interferometer is included to combine light reflected from the wafer surface with a portion of the incoming light at the beamsplitter. The interference pattern formed by that combination is used by the computer to provide real-time manipulation of focus errors, vibration and aberration by deformation of the deformable mirror. The deformable mirror and interferometer system is also applicable to folded beam refractive optic illumination systems and pure refractive optic systems in which a detour is made within the optical train to access the deformable mirror.