Miniature columns or microcolumns are a relatively new class of electron beam columns fabricated entirely from silicon
using advanced micromachining processes. The main characteristics of these columns are thermal field emission (TFE)
sources, low voltage operation (typically <3keV), simple design (two lenses, no crossover), microfabricated lenses, and
all electrostatic components. Current production versions of miniature columns achieve <10nm resolution at 1keV, and
have demonstrated <6nm resolution at higher beam energies.1,2 While this performance is suitable for most applications,
previous studies of the electron optics of miniature electrostatic lenses show better performance should be attainable
under “ideal” conditions.3 In practice, achieving these conditions is challenging because, in addition to the
manufacturing errors from the miniature optics, other subsystems can impose additional constraints. An understanding
of the major contributors to column performance, whether optical or mechanical, is essential, and can provide a roadmap
for further improvements in the existing technology.
Miniature electron beam columns have the advantage of high resolution (<10 nm) at low beam energies (0.5 - 2 kV),
making them well-suited for probing the surface structure of a wide variety of nano-scale materials. Because miniature
columns have the further benefits of small form factor and low cost of manufacturing, they are uniquely suited for high
resolution tabletop Scanning Electron Microscopy (SEM). Miniature columns are also good candidates for use in
multiple beam lithography and high throughput mask writing systems.
A miniature electrostatic column has been developed for the Novelx mySEM tabletop SEM using monolithically
processed bonded stacks of silicon and glass, mounted to a ceramic substrate. It has been shown previously that this
type of design can be used to produce a highly manufacturable and reliable column. This column design has
demonstrated high resolution imaging and lithography capabilities. The column includes a condenser lens integrated
into the source silicon stack, which provides variable beam current density at the limiting aperture in order to vary the
This paper presents results from the condenser lens in the mySEM column, demonstrating continuously variable beam
current over a wide range. Simulations presented in this paper show that this column is capable of >2 nA beam current
using the condenser lens, with only a slight increase in beam size at high beam current. Measurements are in good
agreement with the simulations, demonstrating > 7 nA beam current with the condenser turned on.
The ability to transparently switch optical signals from one fiber to another without conversion to the electrical domain is a basic functionality that has a wide range of applications within the fiber optic industry. The so-called 3D-MEMS architecture has emerged as the preferred approach for building transparent, scalable systems with port-counts ranging from 16x16 to 1024x1024. The primary components of the 3D-MEMS architecture are fiber array, lens array, and MEMS mirror array. While a central theme in the MEMS industry is integration, we adopted a strategy of modularization. The key MEMS components, which include mirror array, ceramic substrate, and high-voltage drivers, were manufactured separately and then combined to yield a working product. Central to our modular approach was critical design parameter tolerancing to ensure manufacturability. Results from a large sampling of MEMS components and MEMS assemblies are presented to highlight manufacturability and performance.
Arrays of field emission micro-cathodes are the basis for massively arrayed electron beam lithography systems. We report on the fabrication of single crystal silicon field emitter arrays that have self-aligned extraction and focusing electrodes. By exposing a `capped' silicon pedestal to a lateral high temperature thermal oxidation, tips of uniform height and profile are formed, with radii of curvature typically less than 20 nm. The field emitters, the first level metal electrodes, and the second level metal electrodes are defined in the same optical lithography step and the first and second level metals are deposited during the same electron beam evaporation. In this fashion, both the extraction and focusing electrodes are formed simultaneously and are self-aligned to the field emitter. Sub-micron first level metal apertures and three micron second level metal apertures have been demonstrated using this process. The diameter of the second level metal electrode is determined by the optical lithography step. It is therefore possible to reduce the second level metal aperture by as much as 1.5 microns before necessitating the use of electron beam lithography. This process is suitable for fabricating self- aligned, second level quadrapole and octapole focusing electrodes.
Optical systems for extreme ultraviolet (EUV) lithography require optical elements with wavefront aberrations limited to a fraction of an EUV wavelength to achieve diffraction-limited performance. Achieving wavefront and surface figure metrology at this level of accuracy is one of the key challenges in the development of EUV lithography. We have successfully built and operated a prototype EUV point diffraction interferometer which is capable of performing wavefront measurement of EUV optical elements at their operational wavelength. Initial experiments to characterize the interferometer, and to measure the optical wavefront diffracted from a Fresnel zone plate lens are discussed.