Temporal drift in the mask manufacturing process has been observed in CD measurements collected at different times. Most of this is corrected through global sizing and dose adjustments resulting in small mean-to-target (MTT) residual errors. However, this procedure does not account for a detectable change in the proximity behavior of the mask process. This paper discusses a procedure for detecting and monitoring the proximity behavior of a process using an targeted sampling plan. It also proposes a procedure to correct for drifts in proximity behavior if it is predictable and systematic.

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