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https://hdl.handle.net/2142/31237
Description
Title
Minimizing electron optical aberrations
Author(s)
Xiu, Kai
Issue Date
2001
Director of Research (if dissertation) or Advisor (if thesis)
Gibson, J. Murray
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
electron microscopy
high resolution electron microscopy (HREM)
SCALPEL
aberration reduction
Language
en
Abstract
"This thesis deals with topics of aberration reduction in high voltage ("""" 100 k V) electron optical
instruments, especially used for lithography (SCALPEL) and high resolution electron microscopy
(HREM).
Since the invention by Berger and Gibson [1) in 1989, SCALPEL (SCattering with Angular
Limitation in Projection Electron-Beam Lithography) has attracted much attention as a candidate
for the next generation lithography (NGL) tool. Like other electron projection systems, its imaging
quality is mainly limited by the optical aberration and space charge effect [2). The former becomes
rapidly dominant with the increase of subfield size and aperture angle, which is, on the other hand,
beneficial to reduce the space charge effect and increase throughput. Among various aberrations,
the field curvature is of the most importance due to its dominant contribution to the blur size for
the image at the edge of an subfield in the SCALPEL projection system [3). Due to this limit, the
simultaneous exposure area on the mask is expect to be confined as small as 1 mm x 1 mm even
in the future commercialized SCALPEL product.
Aberration correction in high resolution electron microscopy is another topic of this thesis.
During recent years, aberration correction in HREM with the aid of multipole lenses has become
feasible in practice [4). Such progress encourages people to improve the HREM with better working
conditions while maintaining extreme resolution power. NTEAM (National Transmission Electron
Achromatic Microscope) which was proposed by Gibson in 1999, represents such an ambitious
project [5) to build a new generation electron microscope capable of sub-A image resolution and sub-electron-volt spectroscopic resolution with adequate space to carry out a variety of important
experiments on advanced materials. There are no doubt enormous challenges for such a project: on
the theoretical side, higher order aberrations in multipole systems were not thoroughly investigated
before; on the practical side, problems such as stray fields and power instability must be overcome
to make the aberration correction meaningful.
In this thesis, we developed new approaches for the aberration correction in high voltage electron
optical instruments. For the SCALPEL projection system, we investigated the extreme aberration
performance of the conventional projection system and proposed a doublet design capable of minimizing
the field curvature under the magnetic round lens scheme. We also discussed the principle
of using space charge to correct the field curvature and show the practical layout of space charge
foils. For HREM, we proposed a quadrupole-octopole-based Cc corrector design suitable for high
resolution TEM with a large gap. We studied various quadrupole-octopole layouts to optimized
the aberration and stability performance and found ways to suppress effects of off-axial and higher
order aberrations in such a design for high resolution goals."
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