Process-window sensitive full-chip inspection for design-tosilicon optimization in the sub-wavelength era

As lithographers continue to implement more exotic and complex resolution enhancement techniques (RET) to push patterning further beyond the physical limits of optical lithography, full-chip brightfield inspections are becoming increasingly valuable to help identify random and systematic defects that occur due to mask tolerance excursions, OPC inaccuracies, RET design errors, or unmanufacturable layout configurations. PWQ, or process window qualification, is a KLA-Tencor product using brightfield imaging inspection technology that has been developed to address the need for rapid full-chip process window verification. PWQ is currently implemented at IBM's 300 mm facility and is being used to isolate features that repeatedly fail as a function of exposure dose and focus errors. We will demonstrate how PWQ results have assisted in: 1) qualification of reticles and new OPC models; 2) identification of non-obvious lithographic features that limit common process windows; 3) providing input for long-term design for manufacturability (DfM), OPC, and/or RET modeling. PWQ allows full or partial chips to be scanned in far less time than a multi-point common process window collected on a SEM. PWQ findings supplement these traditional analysis methods by encompassing all features on a chip, providing more detail on where the process window truly lies. Examples of marginal features that were detected by PWQ methods and their subsequent actions will be discussed in this paper for an advanced 65 nm and a 90 nm CMOS process