Acta Optica Sinica, Vol. 34, Issue 2, 211004 (2014)

In Situ Aberration Measurement Method Based on a Phase-Shift Rings Target

Abstract

An in situ aberration measurement method based on a two-dimensional (2D) phase-shift rings target is proposed for quality evaluation of the lithographic projection lenses. A linear model between aerial-image intensity distribution and wavefront aberrations is built by principal component analysis (PCA) and multivariate linear regression analyses. Compared with the binary target in the AMAI-PCA method, the aerial images of the phase-shift rings contain more information which owns the ability of eliminating crosstalk between different kinds of aberrations, therefore, the accuracies of aberration measurement are improved. Impacts of aerial-image defocus error on the extractions of aberrations are analyzed. A measurement method for defocus error is also proposed. Simulations with the lithographic simulator Dr.LiTHO show that the proposed method can detect 12 terms of Zernike coefficients (Z5~Z16) with maximum error of 1×10-3λ. Simultaneously, the speed of aberration measurement is doubled because less aerial images need to be captured for the merit of applying the new 2D target.

keywords

• aberration measurement
• aerial image
• imaging systems
• microlithography
• phase-shift rings
• principal component analysis