Fourier-synthesis custom-coherence illuminator for extreme ultraviolet microfield lithography

Abstract

Scanning illumination systems provide for a powerful and flexible means for controlling illumination coherence properties. Here we present a scanning Fourier synthesis illuminator that enables microfield extreme ultraviolet lithography to be performed on an intrinsically coherent synchrotron undulator beamline. The effectiveness of the system is demonstrated through a variety of print experiments, including the use of resolution enhancing coherence functions that enable the printing of 50-nm line-space features by use of a lithographic optic with a numerical aperture of 0.1 and an operational wavelength of 13.4 nm.

A design study for synchrotron-based high-numerical-aperture scanning illuminators

“…In conclusion, extending the previously described scanning EUV illuminator concept [11] to use with higher-NA optics and extended field sizes ideally requires the use of a toroidal condenser mirror as well as cylindrical scanning mirrors. The implementation of a compound scanner comprised of two one-dimensional scanners enables a scanning speed increase of approximately a factor of 6 compared to the previously described single-element two-dimensional scanner [11].…”

“…1) [11] was the limited speed of the device forcing exposure times to be on the order of 4 seconds long. This constraint was due to mechanical limitations in the two-dimensional tilt table used as the scanner.…”

“…However, in our particular implementation, the first turning mirror is required for mechanical compatibility with the current beamline and endstation [3,11] installed at sector 12 of the Advanced Light Source. Moreover, in the current beamline configuration, that turning mirror is mounted onto a two-dimensional angle-scanning stage (previously used as the coherence-synthesis scanner), which could now conveniently serve as a field scanner, thereby enhancing the illumination uniformity.…”

“…Here, the desired illumination divergence is effectively synthesized through the scanning process. This method has recently been used at EUV wavelengths to implement a programmable pupil fill microfield exposure system designed to operate with a 0.1-NA lithographic optic [11]. This system, installed at Lawrence Berkeley National Laboratory's Advanced Light Source synchrotron radiation facility, has enabled the early lithographic characterization [3] of an alpha-class EUV stepper optic [12].…”

Performance of actinic EUVL mask imaging using a zoneplate microscope

“…Controlled motion of the beamline optics during an exposure can be used to reduce the coherence 4 : here, a narrow, cone of coherent light moves across an angular range in time, yielding a partially coherent image. We note that when the system is operated with the mask below the focal plane of the Schwarzschild objective, the effective illumination angular range seen by a given point on the mask is reduced (the illumination sweeps past the point).…”