Method and apparatus to characterize photolithography lens quality

A method of characterizing photolithography lens quality, comprising:

• selecting first and second different overlay pattern;
• performing a photolithography simulation to determine a first sensitivity coefficient for the first overlay pattern and a second sensitivity coefficient for the second overlay pattern;
• providing first and second photomasks, the first photomask having the first overlay pattern thereon and the second photomask having the second overlay pattern thereon;
• exposing, with a photolithography tool, first and second wafers with the first and second photomasks to form the first overlay pattern on the first wafer and the second overlay pattern on the second wafer;
• measuring a first relative pattern placement error of the first overlay pattern formed on the first wafer and measuring a second relative pattern placement error of the second overlay pattern formed on the second wafer;
• and
• calculating a quality indicator for a lens in the photolithography tool using the first and second relative pattern placement errors and the first and second sensitivity coefficients.

A system, comprising:

• photolithography simulation tool configured to determine a first sensitivity coefficient for a first overlay pattern and a second sensitivity coefficient for a second overlay pattern;
• a photolithography tool having a lens and an exposure slit, the photolithography tool configured to direct radiation from the exposure slit through a first photomask having the first overlay pattern thereon and onto a first wafer to form the first overlay pattern on the first wafer, the photolithography tool also configured to direct radiation from the exposure slit through a second photomask having the second overlay pattern thereon and onto a second wafer to form the second overlay pattern on the second wafer;
• an overlay metrology tool configured to measure a first relative pattern placement error of the first overlay pattern formed on the first wafer and configured to measure a second relative pattern placement error of the second overlay pattern formed on the second wafer;
• and
• a data processing tool configured to calculate a quality indicator for the lens in the photolithography tool using the first and second relative pattern placement errors and the first and second sensitivity coefficients.