A defocus measurement method for an in situ aberration measurement method using a phase-shift ring mask

An in situ aberration measurement method using a two dimensional (2D) phase-shift ring mask has been proposed for lithographic projection lenses, which is more accurate and faster than AMAI-PCA method. The defocus of the aerial image of the 2D measurement mask is the main source of the measurement error of this method. In this paper, a defocus measurement method for the aberration measurement method is proposed, in which the residual of the principal component analysis process is used as the criterion. After the defocus is accurately measured, the most suitable linear relationship model, which plays a very important role in the aberration measurement method, can be determined. Simulations with the lithography simulator Dr. LiTHO demonstrated that the accuracy of the defocus measurement method is approximately 1nm. The aberration measurement method can detect 12 Zernike aberrations (Z5 about Z16) with maximum systematic error of approximately 1m lambda, when the suitable linear relationship model is used.