14 June 1999 Supersparse overlay sampling plans: an evaluation of methods and algorithms for optimizing overlay quality control and metrology tool throughput
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Abstract
Traditionally, overlay metrology has ben primarily used for quality control of developed wafers. The secondary roles of overlay metrology, stepper modeling and feedback control, have become more prominent in recent years. In particular, the design of overlay sampling plans is usually strongly influenced by the requirements imposed by stepper modeling. Previous research has shown that intrafield sampling plans must be symmetric and repeating in order to support stable feedback control. These constraints impact the tradeoff between overlay tool throughput and quality control by imposing a higher than necessary cost on measuring additional exposure fields for irregular errors. In this paper we examine the concept of using super sparse overlays among plans along with innovative analysis methods and algorithms for stepper modeling. Super sparse sampling plans are defined as where the field by field intrafield sampling is irregular and asymmetric. When compared to typical sampling plans, super sparse plans allow the overlay tool to examine a 2 to 4 times the number of fields on a wafer with the same number of total measurements. In order to support super sparse sampling, it is necessary to employ innovative algorithms, which are capable of performing stepper modeling without losing result integrity. In this paper we report on the relative performance of regular versus super spares sampling plans for quality control, stepper modeling and overlay tool throughput.
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Joseph C. Pellegrini, Joseph C. Pellegrini, Ziad R. Hatab, Ziad R. Hatab, Jeffrey M. Bush, Jeffrey M. Bush, Thomas R. Glass, Thomas R. Glass, } "Supersparse overlay sampling plans: an evaluation of methods and algorithms for optimizing overlay quality control and metrology tool throughput", Proc. SPIE 3677, Metrology, Inspection, and Process Control for Microlithography XIII, (14 June 1999); doi: 10.1117/12.350780; https://doi.org/10.1117/12.350780
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