Method and apparatus for extracting dose and focus from critical dimension data

A system, comprising:

• a photolithography tool operable to generate a feature on a wafer using a commanded dose parameter and a commanded focus parameter;
• a metrology tool operable to measure a top critical dimension of the feature and a bottom critical dimension of the feature;
• a photolithography solver operable to define a model of the photolithography system for modeling top and bottom critical dimension data associated with features formed by the photolithography system as a function of dose and focus, and generate a library of model inversions for different combinations of top and bottom critical dimension values, each entry in the library specifying a dose value and a focus value associated with a particular combination of top and bottom critical dimension values;
• a photolithography monitor operable to receive the top critical dimension measurement and the bottom critical dimension measurement, access the library using the top and bottom critical dimension measurements to generate values for a received dose parameter and the received focus parameter, and compare the received dose and focus parameters to the commanded dose and focus parameters to characterize the photolithography system.