Quantitative phase retrieval with arbitrary pupil and illumination.

Rene A Claus,Laura Waller,Andrew R Neureuther,Patrick P Naulleau

doi:10.1364/oe.23.026672

Rene A Claus, Laura Waller + Show 2 more

Open Access

https://doi.org/10.1364/oe.23.026672

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Abstract

We present a general algorithm for combining measurements taken under various illumination and imaging conditions to quantitatively extract the amplitude and phase of an object wave. The algorithm uses the weak object transfer function, which incorporates arbitrary pupil functions and partially coherent illumination. The approach is extended beyond the weak object regime using an iterative algorithm. We demonstrate the method on measurements of Extreme Ultraviolet Lithography (EUV) multilayer mask defects taken in an EUV zone plate microscope with both a standard zone plate lens and a zone plate implementing Zernike phase contrast.

Highlights

Phase, the cumulative delay of light as it passes through a sample, can provide a wealth of information about a sample
We present a new phase retrieval method that is well suited for such applications and we apply it to measurements of Extreme Ultraviolet Lithography (EUVL) mask defects
While several techniques already use the Weak Object Transfer Function (WOTF) with defocus measurements [21,22,23,24,25], we suggest here that it is possible to use the WOTF with arbitrary measurements where the pupil function or illumination is varied, and we further extend the method to some non-weak objects

Summary

Introduction

The cumulative delay of light as it passes through a sample, can provide a wealth of information about a sample. Most quantitative phase recovery techniques in conventional microscopes involve multiple measurements taken as either the pupil function, the illumination, or both are changed. Under the assumption of a weakly scattering object, it is possible to calculate the Weak Object Transfer Function (WOTF) / Contrast Transfer Function (CTF) to relate the intensity and field Note that this transfer function describes the spatial frequency content of the phase information which can be measured by intensity images. The programmable illumination, ease of changing the pupil function using zone plates, and the generally weak phase nature of features on EUV masks makes this a well suited application for our algorithm. The scattered light consists of everything else and describes the structure of the object This can be understood by considering the simple case of the intensity at the image plane under coherent illumination.

Deriving the weak object transfer function

Findings

Conclusion