Evaluations of CD-metrology tools usually focus on resolution, repeatability and accuracy. These are traditional metrics which relate to the capability to measure a local line width. These metrics do not cover the capability to map the CD fingerprint (uniformity map) of the wafer and scanner field, which are essential for sub-100nm lithography process control. In this study, CD-uniformity wafers of state-of-the-art step-and-scan systems were measured with different metrology tools. Analysis of the results revealed a random contribution that could not be attributed to the exposure tool or to the repeatability of the metrology tool. A test and analysis method was developed to separate out this random contribution from the test results. The level of this random CD variation, called the Total Test Repeatability (TTR), is proposed here as a new metric to compare CD-metrology tools in their capability to generate CD uniformity maps. The method was applied to study CD-SEM, Electrical Line width Measurements and CD-scatterometry. In general, the TTR appears to be much larger than the metrology tool repeatability. As such it is an important figure of merit for CD metrology tools used to reveal fingerprints of reticles, exposure tools or processing tools. The TTR is dependent on the metrology tool, measurement algorithm, but also on materials and processing flow and conditions. Some root causes have been identified, such as the wafer resistivity properties for ELM or line width roughness that appears as CD variation in CD-SEM tools. Modifications can be made in the metrology strategy to suppress the TTR and reveal more reliable CDuniformity fingerprints.

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We report here on initial results for the characterization and modeling of 1 00 nm lithography features based on normal incidence spectroscopic ellipsometry and polarized reflectometry. In this work, a set of wafers was exposed as focusexposure and separate focus or exposure matrices to create resist patterns with extremely small variations in CD and pattern shape. These variations were generated along scan, within slit and across full wafer. Optical CD scatterometry was used to extract critical feature paranters such as complete shape and associated linear dimensions. Extracted pattern parameters were compared to FIB xsections and used to predict lithography process latitudes. We explore effects of using multiple normal incidence ellipsometric signals with various profile models to increase accuracy of extracted lithography parameters. We propose a metric for identifying effects of scan-dynamic dose and focus variations upon slit-intrafield and scan-intrafield CD errors. This has been tested over ranges of defocus and exposure that are larger than typical FE latitudes of 1 00 nm features. As a result of spectroscopic scatterometry calculations of pattern shape, we identified pattern shape variations caused by dose and defocus that are clearly coupled to changes in feature size. These could be used for unique determination of dose-focus deviations using scatterometry-extracted information from measurements of a grating structure

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