Patent ID: 7085676

Claim:
A method of measuring feature parameters on a wafer in a microelectronic fabrication process, comprising the steps of: taking a first optical metrology measurement at a feature location on a wafer after a first step in a fabrication process; determining first parameters for the feature location from the first optical metrology measurement, said determining step including comparing the measurement to theoretical optical results calculated from a first theoretical model of the wafer using a first set of theoretical parameters; taking a second optical metrology measurement at the same feature location after a subsequent step in the fabrication process; and determining second parameters for the feature location from the second optical metrology measurement, said determining step including comparing the measurement to theoretical optical results calculated from a second theoretical model of the wafer using a second set of theoretical parameters in combination with at least one of the previously determined first parameters used as a fixed parameter thereby reducing the number of fitting parameters needed to determine the second parameters.