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This paper outlines a technique for determining the sampling capability ratio (Csk)for overlay metrology and the implementation into the manufacturing line. This technique is analogous to the traditionally used process capability ratio (Cpk) with modifications to account for the systematic nature of misalignment. Specifically, the Csk analysis is based only on historical data which was available for metrology skips, uses modeled systematic data, and uses a statistical analysis based on the lognormal distribution including confidence intervals, and normality checking. In addition, upgrades to the statistical process control (SPC) strategy in photolithography are outlined as well as a future upgrade to the current system known as adaptive sampling.
Date of Conference: 4-6 May 2004