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Abstract

Measurement apparatus and procedure for use with lithographic equipment is provided for the construction of electronic and other devices wherein a photoresist is deposited as a layer upon a substrate. A Nomarski differential interference contrast microscope in conjunction with a scanned image detector is employed to examine verification marks produced by projection of an overlay, such as the mask or reticle, upon the photoresist layer. The projection results in a production of verification marks in the form of a latent image which, while invisible with conventional viewing means, can be viewed by phase-contrast imaging employing differential phase shift. Various characteristics of the resultant image are employed to align secondary verification marks with primary verification marks previously provided on the substrate, and to allow for a checking of line width, dosage, focusing, temperature control, and global alignment. Observation of the photoresist is accomplished with radiation at lower frequency than the exposure radiation, the latter being significantly absorbed, by the photoresist, the photoresist being transparent to the observation radiation to permit reflection from top and bottom surfaces of the photoresist.

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First Claim