Automated process control using parameters determined from a photomask covered by a pellicle

A computer-readable storage medium containing computer-executable instructions to control a photolithography cluster using optical metrology, comprising instructions for:

• a) obtaining a set of different values of one or more photomask structure parameters, the photomask covered with a pellicle;
• b) obtaining a set of diffraction signals using the set of different values of the one or more photomask structure parameters;
• and
• c) training a machine learning system using the set of diffraction signals as inputs to the machine learning system and the set of different values of the one or more photomask structure parameters as expected outputs of the machine learning system.
• (d) obtaining a measured diffraction signal off the structure to be examined;
• (e) after the machine learning system has been trained, inputting the measured diffraction signal into the machine learning system to obtain one or more values of one or more photomask structure parameters as an output of the machine learning system;
• and
• (f) adjusting one or more process parameters or equipment settings of a fabrication cluster based on the one or more values of the one or more obtained structure parameters.

A system to control a photolithography cluster using optical metrology, the system comprising:

• a photolithography cluster configured to perform a photolithographic process to fabricate a structure on a wafer;
• an optical metrology system comprising:
• a beam source and detector configured to measure a diffraction signal off a photomask structure covered with a pellicle;
• a processor connected to the beam source and detector, wherein the processor is configured to compare the measured diffraction signal to a simulated diffraction signal off the photomask structure, wherein the simulated diffraction signal is associated with one or more values of one or more photomask structure parameters, wherein the simulated diffraction signal was generated using one or more values of one or more photomask structure parameters;
• and
• a metrology processor coupled to the optical metrology system and the photolithography cluster, wherein the metrology processor is configured to adjust one or more process parameters or equipment settings of the photolithography cluster based on the one or more values of the one or more photomask structure parameters determined by the processor of the optical metrology system.