Overlay metrology sampling capability analysis and implementation in manufacturing

This paper outlines a technique for determining the sampling capability ratio (C/sub sk/)for overlay metrology and the implementation into the manufacturing line. This technique is analogous to the traditionally used process capability ratio (C/sub pk/) with modifications to account for the systematic nature of misalignment. Specifically, the C/sub sk/ 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.