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US 6,587,282 B1Granted
Broadband refractive objective for small spot optical metrology
AssigneeTherma-Wave, Inc.
InventorsDavid Y. Wang, David M. Aikens
Life of this patent
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AssigneeTherma-Wave, Inc.
InventorsDavid Y. Wang, David M. Aikens
Estimating the term…
The subject invention relates to broadband optical metrology tools for performing measurements of patterned thin films on semiconductor integrated circuits. Particularly a family of optical designs for broadband, multi-wavelength, DUV-IR (185<λ<900 nm) all-refractive optical systems. The designs have net focusing power and this is achieved by combining at least one positively powered optical element with one negatively powered optical element. The designs have small spot-size over the wavelength range spanning 185-900 nm with substantially reduced spherical aberration, axial color, sphero-chromatism and zonal spherical aberration. The refractive optical systems are broadly applicable to a large class of broadband optical wafer metrology tools including spectrophotometers, spectroscopic reflectometers, spectroscopic ellipsometers and spectroscopic scatterometers.
A refractive objective of focal length F comprising a first positive lens made from a first optical material, a second negative lens made from a second optical material and a third positive lens made from a third optical material, the lens elements are specified according to a prescription where the lens faces are consecutively designated from the front to the rear as the first to the sixth face, where rn is the radius of curvature of the nth face and tn is the distance between the nth and (n+1)st face, the elements are arranged in a configuration where:
Dependencies are inferred from the claim text.