Laser-based wafer measuring system

摘要

An optical system and associated electronic processing for measuring 0.5-micron and larger dimensions on sample wafers by transversely moving the sample under a stationary microspot provided by a tightly-focused ultraviolet ("UV") laser beam and detecting the interaction of the laser microspot with the sample. The optical system includes a high numerical aperture objective close to the sample surface, a first UV optical train, a second UV optical train, and a UV detector. The first train transports the laser beam to the objective for focusing at the sample surface. The second train communicates UV light emanating from the surface and passing through the objective to the UV detector. The second optical train preferably includes a pinhole which provides added spatial resolution, both laterally and vertically. Light emanating from scattering centers laterally away from the spot or from deeper layers within the wafer focus at different points and are blocked by the edges of the pinhole.