Phase-shifting test mask patterns for characterizing illumination polarization balance in image forming optical systems

Abstract

A method to monitor the state of polarization incident on the photomask in projection printing is presented. The method includes a series of phase-shifting mask patterns that take advantage of high NA effects to create a signal dependent on only one incident polarization component. The patterns exist in two embodiments: a Radial Phase Grating (RPG) and Proximity Effect Polarization Analyzers (PEPA). The PEPAs are derived from basic principles and are theoretically the most sensitive patterns to polarization. A polarimeter is then constructed of six patterns of either embodiment that, when properly calibrated, is sufficient to measure the Stokes parameters of the incident illumination. A test reticle design is proposed, consisting of multiple polarimeters with an array of pinholes on the backside of the photomask. This technique is able to monitor any arbitrary illumination scheme for a particular tool. Calibration of the test mask is required. However, proper calibration is likely to enable accurate full pupil polarization characterization, even when severe mask topography effects and reasonable maskmaking limitations are considered.

Dependencies are inferred from the claim text.