Patent ID: 9594309
Date: 2017-03-14
CPC Classifications: G03F

Claim:
1. A method of characterizing photolithography lens quality, comprising: selecting first and second different overlay patterns, each of the first and second overlay patterns having a first feature with a first pitch and a second feature with a second pitch different than the first pitch; 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, the first and second sensitivity coefficients being respectively associated with a first lens aberration pattern represented by a first Zernike coefficient and a second lens aberration pattern represented by a second Zernike coefficient different than the first Zernike coefficient; 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 solving a system of Zernike polynomial equations using the first and second relative pattern placement errors and the first and second sensitivity coefficients to determine values for the first and second Zernike coefficients.