A novel cold cathode field emission array (FEA) X-ray source based on ultra-nanocrystalline diamond (UNCD) field emitters is being constructed as an alternative for detection of obscured objects and material. Depending on the geometry of the given situation the flat-panel X-ray source could be used in tomography, radiography, or tomosynthesis. Furthermore, the unit could be used as a portable X-ray scanner or an integral part of an existing detection system. UNCD field emitters show great field emission output and can be deposited over large areas as the case with carbon nanotube “forest” (CNT) cathodes. Furthermore, UNCDs have better mechanical and thermal properties as compared to CNT tips which further extend the lifetime of UNCD based FEA. This work includes the first generation of the UNCD based FEA prototype which is being manufactured at the Center for Nanoscale Materials within Argonne National Laboratory with standard microfabrication techniques. The prototype is a 3x3 pixel FEA, with a pixel pitch of 500 μm, where each pixel is individually controllable.
A novel x-ray source based on carbon nanotubes (CNTs) field emitters is being developed as an alternative for medical
imaging diagnostic technologies. The design is based on an array of millions of micro sized x-ray sources similar to the
way pixels are arranged in flat panel displays. The trajectory and focusing characteristics of the field emitted electrons,
as well as the x-ray generation characteristics of each one of the proposed micro-sized x-ray tubes are simulated. The
electron field emission is simulated using the OOPIC PRO particle-in-cell code. The x-ray generation is analyzed with
the MCNPX Monte Carlo code. MCNPX is used to optimize both the bremsstrahlung radiation energy spectra and to
verify the angular distribution for 0.25-12 μm thick molybdenum, rhodium and tungsten targets. Also, different
extracting, accelerating and focusing voltages, as well as different focusing structures and geometries of the micro cells
are simulated using the OOPIC Pro particle-in-cell code. The electron trajectories, beam spot sizes, I-V curves,
bremsstrahlung radiation energy spectra, and angular distribution are all analyzed for a given cell. The simulation results
show that micro x-ray cells can be used to generate suitable electron currents using CNT field emitters and strike a thin
tungsten target to produce an adequate bremsstrahlung spectrum. The shape and trajectory of the electron beam was
modified using focusing structures in the microcell. Further modifications to the electron beam are possible and can help
design a better x-ray transmission source.
Debris generation in EUV sources is a real threat to the lifetime of collector optics. Debris measurements in these
sources are of immense importance to enable source suppliers to estimate collector lifetime. Ion debris measurements
performed so far are not consistent and in part incomplete. To verify lifetime claims from different EUV source
suppliers, SEMATECH, which is leading this investigation, has collaborated with and provided funding to the Center for
Plasma Material Interactions (CPMI) at the University of Illinois to build a fully calibrated and standardized spherical
sector electrostatic energy analyzer (ICE). This device is capable of measuring ion debris flux in absolute units. In
addition to ion flux, the detector is also capable of identifying different ion species present in the plasma, which can be
discriminated based on energy-to-charge ratio. The lifetime of collector optics is calculated using the measured ion flux.
This device was fabricated for SEMATECH with the sole aim of traveling to different EUV source suppliers' sites
around the world and collecting ion debris data. SEMATECH has measured ion debris from different EUV sources
around the world, using a 1 to 14keV ion energy range under different source operational conditions (chamber pressure,
pinch frequency, pinch power, angle). These measurements identify the need for debris mitigation in all the EUV
sources investigated under this project. They also give source suppliers an opportunity to improve and optimize the
performance of their respective sources. The information on absolute ion fluxes is an advantage to source suppliers,
allowing them to design and develop effective debris mitigation schemes, which can again be tested for their
effectiveness using the ion diagnostic tool. As the debris consists of ions and neutrals, the next logical step is to develop
a standardized neutral detector to measure the flux and energy distribution of neutrals present in EUV plasma sources.
Taking into account both ions and neutral fluxes, more definitive conclusions on the performance of a EUV source can
be made and better collector lifetime estimation models can be derived. The Illinois Calibrated ESA (ICE) tool is now
part of the SEMATECH "Flying Circus" equipment set.