Abstract: A target for measurement of critical dimension bias on a substrate formed by a lithographic process comprises six contrasting arrays of elements on first and second layers of the substrate. Each of the arrays has a plurality of spaced parallel elements contrasting with the substrate. Ends of the contrasting elements are aligned along parallel lines forming opposite array edges, with the length of the contrasting elements comprising the array width. The array edges are measurable by microscopy without resolution of individual elements of the array. The arrays are spaced apart in the X-direction, with three on a first layer of the substrate and three on a second layer of the substrate. The first, second and third contrasting arrays of elements on the first layer of the substrate are interposed between at least two of the fourth, fifth and sixth contrasting arrays of elements on the second layer of the substrate.

Abstract: A method for monitoring a process in which a feature is formed on a substrate. A plurality of dimensions of the feature are measured using a tool. An edge width of the feature is calculated based on the plurality of dimensions. The edge width is used to determine whether the process is operating within a desired specification. The calculated edge width is compared to a baseline edge width measurement to determine a difference between them. The process is determined to be operating within the specification if the difference is less than a threshold value. If the difference is greater than or equal to the threshold value, the method determines whether the difference is caused by a change in resolution of the tool. A plurality of diagnostic measurements of the edge width may be performed. The tool is adjusted to have a respectively different focus for each respective one of the plurality of diagnostic measurements.