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Title:Minimizing electron optical aberrations
Author(s):Xiu, Kai
Director of Research:Gibson, J. Murray
Department / Program:Physics
Subject(s):electron microscopy
high resolution electron microscopy (HREM)
aberration reduction
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.
Issue Date:2001
Genre:Dissertation / Thesis
Rights Information:© 2001 Kai Xiu
Date Available in IDEALS:2012-05-23
Identifier in Online Catalog:4539121

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