Optimized characterization of wafers structures for optical metrology

A method of modeling structures for optical metrology, the structures including a patterned structure and an unpatterned structure, the method comprising:

• a) setting one or more diffraction sensitivity enhancement termination criteria;
• b) creating a first optical metrology model corresponding to the unpatterned structure;
• c) generating a first simulated diffraction signal for the unpatterned structure using the first optical metrology model;
• d) creating a second optical metrology model corresponding to the patterned structure, wherein the patterned structure has a treated portion and an untreated portion, and wherein one or more properties of the patterned structure was adjusted using one or more diffraction sensitivity enhancement techniques to enhance diffraction contrast between the treated portion and the untreated portion of the patterned structure;
• e) generating a second simulated diffraction signal for the patterned structure using the second optical metrology model;
• f) calculating a diffraction sensitivity enhancement value using the first and second simulated diffraction signals;
• and
• g) comparing the calculated diffraction sensitivity enhancement values to the set one or more diffraction sensitivity enhancement termination criteria.

A system for modeling a wafer structure processed with a diffraction enhancement technique, the system comprising:

• a fabrication cluster configured to apply one or more diffraction enhancement techniques to a patterned structure on a wafer and an unpatterned structure on the wafer;
• a metrology cluster configured to measure diffraction signals off the unpatterned and the patterned structures after the one or more diffraction enhancement techniques are applied;
• a diffraction enhancement selector configured to compare the diffraction signal off the unpatterned and the patterned structures after the one or more diffraction enhancement techniques are applied, determine if one or more diffraction enhancement termination criteria are met, and transmit the diffraction enhancement information;
• and
• a model optimizer coupled to the diffraction enhancement selector and the metrology cluster, the model optimizer configured to optimize an optical metrology model of the patterned structure using the diffraction enhancement information and a profile model of the patterned structure.

A computer-readable storage medium containing computer executable code to select diffraction orders of a diffraction signal for use in optical metrology by instructing the computer to operate as follows:

• a) setting one or more diffraction sensitivity enhancement termination criteria;
• b) obtaining a first diffraction signal measured off an unpatterned structure on a wafer using an optical metrology device;
• c) obtaining a second diffraction signal measured off an patterned structure on the wafer using the optical metrology device, wherein the patterned structure has a treated portion and an untreated portion, and wherein one or more properties of the patterned structure was adjusted using one or more diffraction sensitivity enhancement techniques to enhance diffraction contrast between the treated portion and the untreated portion of the patterned structure;
• d) calculating a diffraction sensitivity enhancement value using the first and second diffraction signals;
• and
• e) comparing the calculated diffraction sensitivity enhancement values to the set one or more diffraction sensitivity enhancement termination criteria.

A computer-readable storage medium containing computer executable code to model wafer structures for use in optical metrology by instructing the computer to operate as follows:

• a) setting one or more diffraction sensitivity enhancement termination criteria;
• b) creating a first optical metrology model corresponding to the unpatterned structure;
• c) generating a first simulated diffraction signal for the unpatterned structure using the first optical metrology model;
• d) creating a second optical metrology model corresponding to the patterned structure, wherein the patterned structure has a treated portion and an untreated portion, and wherein one or more properties of the patterned structure was adjusted using one or more diffraction sensitivity enhancement techniques to enhance diffraction contrast between the treated portion and the untreated portion of the patterned structure;
• e) generating a second simulated diffraction signal for the patterned structure using the second optical metrology model;
• f) calculating a diffraction sensitivity enhancement value using the first and second simulated diffraction signals;
• and
• g) comparing the calculated diffraction sensitivity enhancement values to the set one or more diffraction sensitivity enhancement termination criteria.