Abstract: A significant contributor to linewidth control in a step and scan system is the focal plane nonuniformity. The various sources contributing to this focus nonuniformity such as wafer and reticle flatness will be discussed. Effective wafer flatness presented in the form of flatness variation histograms, as a function of focus sensor fill factor will be presented. A clear understanding of the effective wafer plane flatness variation is important in predicting lithographic tool linewidth control performance. Statistical approaches using joint probability distributions to combine various error sources will be developed. Data will be presented to show that the systematic error sources can be represented reasonably well by uniform distributions, and random error sources by Gaussian distributions. It will also be shown that the focal system performance estimated using this approach could accurately predict system performance and its impact on linewidth control. This allows determination of significant contributors to the focal plane nonuniformity, which is important in establishing the lithographic tool areas of improvements. Data illustrating the influence of contributors such as wafer and reticle flatness, and optical field curvature on linewidth control will presented together with a statistical metrology for incorporating them into a meaningful focal plane error budget. !0
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