Focus spot detection method and system

摘要

A method and system for detecting focus spots. Data from a file created during stepper operation is extracted to get field coordinate position, leveling scheme, and tilt with respect to the x- and y-axes, and wafer height with respect to the focal plane for the multiple fields on the multiple wafers in a production batch. A delta value is calculated for the x- and y-axes tilt data which averages the tilt of each field with its surrounding fields. Delta values are placed in a 3-dimensional data structure linking neighboring fields and corresponding fields on subsequent wafers. Focus spots are detected by the repeated presence of data spikes over the sum of the arithmetic mean and some multiple of the standard deviation of the delta values.