2 June 2003 Effect of bias variation on total uncertainty of CD measurements
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Measurement precision to process tolerance ratio (P/T) is an essential indicator of metrology readiness for a specific technology. A smaller ratio improves the process control achievable with a given metrology. The International Technology Roadmap for Semiconductors is calling for P/T of 0.2. The 'precision' (P) represents total uncertainty of the measurement. In practice P is estimated as the total variation of measurements made on a reference sample(s) over an extended period of time. This procedure leaves sample-to-sample variation of measurement bias outside of P (measurement bias is the difference between reported average and true value). We report on sample-to-sample CD SEM bias variation as characterized by CD AFM. CD AFM is virtually immune to material, layout and line profile variations and, therefore, is expected to have negligible sample-to-sample bias variation. We found that sample-to-sample CD SEM measurement bias variation (full range up to 15 nm) is often comparable to or even exceeds CD SEM reproducibility (full range of ~ 3 nm). Therefore, the current methodology of the 'precision' measurement is leaving a significant component of the total measurement uncertainty unaccounted. The sample-to-sample bias variation measured on a set of samples representative to the specific technology needs to be corrected or added to the tool reproducibility in order to estimate total uncertainty of measurement. This may noticeably change the 'precision' of CD SEM and move P/T for the current 130 nm and 100 nm technologies well over the limit of 0.2. Should the industry keep CD SEM as a major in-line CD across chip metrology the sample-to-sample bias variation has to be significantly improved. Otherwise, chip manufacturers will likely fail to deliver required across chip gate CD uniformity.
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Vladimir A. Ukraintsev, Vladimir A. Ukraintsev, } "Effect of bias variation on total uncertainty of CD measurements", Proc. SPIE 5038, Metrology, Inspection, and Process Control for Microlithography XVII, (2 June 2003); doi: 10.1117/12.483512; https://doi.org/10.1117/12.483512


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