Erik Anderson
Department of Materials Sciences,
Lawrence Berkeley National
Lab
Abstract:
Because the phase shift per unit of attenuation is insufficient in the x-ray
region of the electromagnetic spectrum to make conventional transmission lenses,
Fresnel zoneplates which are circular grating-like diffractive nanostructures
are used to focus and image x-rays. The diffraction-limited resolution is
approximately equal to the half pitch of the outer zones, so fine pitch
nanofabrication processes are needed for high-resolution applications.
Additionally, aberrations caused by imperfections in the zone placement
must be minimized. Due to the demanding requirements posed by x-ray microscopy
in terms of linewidth, dense patterns, and placement, a specialized electron
beam lithography system was developed optimized for curved high-resolution
diffractive structures, as opposed to rectilinear structures commonly found
in other applications. This system, called the nanowriter, operates at 100KeV,
has a pattern generator that produces curved shapes supported at a low level
in hardware, and has unique alignment and image processing based overlay algorithms.
The system will be described in detail as well as many applications of zone plates
for imaging, focusing, and manipulation of soft x-rays. A key application of zone plates
is to x-ray microscopy. Using double patterning to mitigate the forward scattering effect
and image processing based alignment to allow for 2nm or less overlay errors, 15nm outer
zone width zone plates have been fabricated and tested. Zone plates for both scanning and
full field have been developed as well as variations on the basic zone plate to extend
properties such as depth of focus and chromatic aberrations. These variations introduce
well-controlled phase structure to the basic zone plate for wavefront coding and computer
image processing recovers the original image. Ongoing efforts to extend the resolution
into the sub-10nm regime will be described.
2008 Run
Nov 19th - Dec 22nd
