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Abstract

An optical apparatus used for the efficient characterization of photoresist material includes at least one grating interferometer having at least two gratings that together define an optical recombination plane. An optical stop blocks any zeroth order beam from propagating through the apparatus. A reticle positioned at the recombination plane has at least one fiducial marking therein. A lithographic imaging optical tool is positioned so that its input optical plane is substantially coincident with the optical recombination plane and its output imaging plane is substantially coincident with photoresist on a wafer. The apparatus writes in the photoresist latent, sinusoidal grating patterns, preferably of different spatial frequencies, as well as at least one fiducial mark whose pattern is determined by the marking in the reticle. After the photoresist is developed, its intrinsic spatial resolution may be determined by automated means.

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