Illumination control in lensless imaging for EUV mask inspection and review

Abstract

Coherence control and flexible pupil fill play a key role in the imaging of EUV reticles. This is also true for lensless metrology applications based on coherent diffraction imaging. We describe the concept and the key components of a Fourier synthesis illuminator designed to provide the RESCAN microscope with flexible illumination capabilities and to improve its resolution limit. In particular, we discuss the characteristics of the three mirrors of the new illuminator and the requirements for their multilayer coating.

Lensless EUV mask inspection for anamorphic patterns

“…This helps to overcome the geometrical limit set by the illumination optics and the reflectance loss caused by the multilayer for diffraction angles larger than 12 degrees. 10 The opposite behavior is observed for a pattern with the inverse aspect ratio (Fig. 3B).…”

High resolution and uniform image reconstruction in a large field-of-view for EUV actinic mask review

“…Furthermore, this implemented correction method removes the focal gradient, and thereby the reconstructed image FOV is enlarged, which allows for flexible post data processing. These improvements can also be applied for our plan to upgrade the RESCAN for high NA APMI toward below 5 nm EUVL node [10].…”

“…Also, throughpellicle imaging was demonstrated in RESCAN last year [9]. We currently plan an upgrade of the tool towards < 20 nm defect resolution to meet the 5 nm EUVL technology node and below [10].…”

Resolution limit and photon flux dependency in EUV ptychography

“…Accurate imaging of the extreme ultraviolet (EUV) mask is essential in EUV lithography. At Paul Scherrer Institute (PSI), we are developing RESCAN (Reflection-mode EUV SCANning microscope), a ptychography-based microscope dedicated to actinic patterned mask inspection (APMI) [1][2][3][4]. It is a synchrotron-based platform installed at the XIL-II beamline of the Swiss Light Source (SLS).…”