Patent ID: 7369697

Claim:
A method for producing an empirical estimator of a process variable of interest, comprising: selecting a process variable of interest to monitor through a selected process window; printing at least one feature of interest on a surface of a substrate with a change in the process variable of interest commanded over the selected process window; generating an image of the feature of interest using a microscope-based metrology tool; collecting numerical values for at least one image attribute of the feature of interest over the exercised process window; and establishing a correlation of the image attribute to the process variable of interest to produce an empirical estimator of the process variable of interest, said empirical estimator having a formula ((v i j *b 1 -v i′ j′ *a 1 )-(a 3 *b 1 -b 3 *a 1 ))/(a 2 *b 1 - b 2 *a 1 ), wherein v i j and v i′ j′ are values of two image attributes and a 1 , a 2 , a 3 are constants derived from a least squares fit of a second order polynomial to the experimental data for v i j vs. focus and dose, and b 1 , b 2 , b 3 are constants derived from the least squares fit of a second order polynomial to experimental data for v i′ j′ vs. focus and dose.