Propagation-based phase retrieval using the contrast transfer function (CTF) allows images at any propagation distance to be used when recovering the phase of slowly-varying objects. The CTF suffers from artifacts due to nulls in the transfer function at low spatial frequency and at higher, propagation-distance-dependent frequencies, though the latter can be alleviated by combining measurements at multiple distances. We demonstrate that the use of extended sources can improve low frequency performance. In addition, this method offers source shape as a parameter that can be used when optimizing combinations of measurements to produce robust phase reconstructions.
Propagation-based phase contrast using the transport of intensity equation (TIE) allows rapid, deterministic phase retrieval from defocused images. For weakly attenuating objects, phase can be retrieved from a single image. However, the TIE suﬀers from significant low frequency artifacts due to enhancement of noise during phase retrieval. We demonstrate that by patterning the illumination source as approximately a modified Bessel function of the 2nd kind of zero order, quantitative phase can be imaged directly at the detector within a spatial frequency band. Outside of that band, Bessel sources still improve low frequency performance in phase retrieval.
In this paper, we present the first results of witness sample based outgas resist family test to improve the efficiency of outgas testing using EUV resists that have shown proven imaging performance. The concept of resist family testing is to characterize the boundary conditions of outgassing scale from three major components for each resist family. This achievement can significantly reduce the cost and improve the resist outgas learning cycle. We also report the imaging performance and outgas test results of state of the art resists and discuss the consequence of the resist development with recent change of resist outgassing specifications. Three chemically amplified resists selected from higher outgassing materials are investigated, but no significant improvement in resist performance is observed.
EUV lithography is a technology enabling next generation electronic devices, but issues with photoresist sensitivity,
resolution and line edge roughness as well as tool downtime and throughput remain. As part of the industry's efforts to
address these problems we have worked with resist suppliers to quantify the relative contamination rate of a variety of
resists on EUV multilayer mirror analogues following ASML approved protocols. Here we present results of our
ongoing program to better understand the effect of process parameters such as dose and resist thickness on the
contamination rate of ruthenium coated witness plates, additionally we present results from a study on the effectiveness
of hydrogen cleaning.
Characterization of defects and their sources is essential for developing mitigation solutions to support the
production of defect-free extreme ultraviolet (EUV) mask blanks. Enhancements to cleaning processes and the
deposition tool are proving to decrease the defect density on mask blanks, and the resulting defect trends can be
tracked to determine the effectiveness of these improvements. While standard defect characterization methods such
as atomic force microscopy (AFM) and scanning electron microscopy (SEM) can provide useful information for
large defects, sub-100 nm defects pose challenges to the current conventional metrology techniques. To address the
study of these nanoscale defects, SEMATECH's Mask Blank Development Center (MBDC) houses advanced
metrology capabilities that include Auger electron spectroscopy (AES) and high resolution transmission electron
microscopy (TEM). Both techniques are providing enhanced compositional analysis capabilities for defect
reduction efforts. TEM is proving to be a valuable technique for defect mitigation and is currently supporting many
other projects including substrate smoothing activities, deposition simulation development, and defect printability
studies. The rising issues with the metrology of increasingly small EUV mask blank defects will be outlined, and
comprehensive characterization results using TEM and AES on EUV mask blank defects will be presented.