Abstract
We demonstrate a method for characterizing the field-dependent aberrations of a full-field synchrotron-based extreme ultraviolet microscope. The statistical uniformity of the inherent, atomic-scale roughness of readily-available photomask blanks enables a self-calibrating computational procedure using images acquired under standard operation. We characterize the aberrations across a 30-um field-of-view, demonstrating a minimum aberration magnitude of smaller than lambda /21 , {hbox {rms}} averaged over the center 5-um area, with a measurement accuracy better than lambda /180 , {hbox {rms}}. The measured field variation of aberrations is consistent with system geometry and agrees with prior characterizations of the same system. In certain cases, it may be possible to additionally recover the illumination wavefront from the same images. Our method is general and is easily applied to coherent imaging systems with steerable illumination without requiring invasive hardware or custom test objects; hence, it provides substantial benefits when characterizing microscopes and high-resolution imaging systems in situ.
Highlights
Method is data-efficient; in our implementation, we use 10 speckle images to recover all field-varying aberrations of up to order 5
We are able to reconstruct the field-dependent aberrations of a full-field extreme ultraviolet (EUV) microscope using the atomic-scale roughness of photomask blanks and no additional hardware
Our results demonstrate that SHARP achieves diffraction-limited performance, with wavefront errors below /21 averaged over the center 5 μm×5 μm region of the total captured field-of-view
Summary
Experiments were performed on the SHARP microscope at Lawrence Berkeley National Laboratory’s Advanced Light Source (ALS). SHARP is a synchrotron-based, full-field EUV microscope designed to emulate aerial image formation in industrial EUV photolithography scanners. We collected 10 coherently illuminated images of the photomask blank (Fig. 2). An image taken with central illumination and a large defocus was used to estimate speckle properties. The other 9 images were acquired with varying illumination angles near the central ray angle. The choice of these angles is discussed
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