Abstract
The extension of optical lithography to 32 nm and beyond is dependent on double-patterning at critical levels. Double patterning adds degrees of freedom for overlay variation while reducing the allowed overlay tolerance. Overlay control requires the assessment and minimization of error among various mask/layer combinations. The possible overlay control combinations scale as Cn=(2n−1)2 with the number of reference layers n containing (x,y) alignment and overlay targets. Finding the optimum overlay control pathway requires that we employ the on-product means to examine multiple options compatible with the product overlay tolerances. The Blossom overlay target enables simultaneous determination of all combinations of patterns represented within the measurement tool field of view. We examine Blossom enabled use cases in double patterning overlay control as demonstrated at contact-to-gate registration on a 32 nm product.
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