Particle contamination is analyzed for a reticle in the inner pod of a carrier with particular emphasis on the effect of
raising the cover of the inner pod before removing the reticle from the carrier at atmospheric pressure (not low pressure).
Two mechanisms for particle transport into the gap between the base plate and the reticle are considered: injection and
advection-diffusion. It is shown that injection is not an important mechanism but that advection-diffusion transport can
carry particles deeply into the gap, where they can deposit on the reticle surface. Closed-form expressions are presented
for the transmission probability that particles at the reticle edge are transported inward past the exclusion zone around
the reticle perimeter. The gas flow in the gap that occurs during cover-raising is found by numerical simulation, and the
closed-form expressions are applied to determine the probability of contamination for different cover-raising scenarios.
A 'thermophoretic pellicle' has been proposed as an alternative to the traditional organic pellicle as a means of protecting EUV lithographic photomasks from particle contamination. The thermophoretic pellicle protects a mask from particles by exploiting the thermophoretic force, which is exerted on a particle by a surrounding gas in which a temperature gradient exists. Two critical requirements of the thermophoretic pellicle are: 1) the mask is kept warmer than its surroundings (either by heating the mask or by cooling the surroundings) and 2) the surrounding gas pressure is kept sufficiently high to enable thermophoretic protection. Experiments are presented which verify the viabilitiy of thermophoretic protection for EUV masks under model conditions. In these experiments, wafers are exposed to monodisperse polystyrene latex (PSL) spheres under carefully controlled experimental conditions. Robust thermophoretic protection is observed over a wide range of argon gas pressures (50-1600 mTorr or 6.66-213 Pa), particle sizes (65-300 nm), and temperature gradients (2-15 K/cm).
A prototype of an unattended ground sensor has been developed for detection of biological agent aerosols. This point sensor uses ultraviolet laser induced fluorescence (UV LIF) to detect aerosol biological microorganisms collected on filter media. The concept can be designed to be compact, low power, and hardened to survive harsh delivery environments such as airdrop. The prototype consists of an air sampling system, a filter exchange mechanism, an Nd:YAG microlaser that is frequency tripled and quadrupled to generate 355-nm and 266-nm excitation wavelengths, a spectrometer, an intensified CCD detector, and a data acquisition and control system. The analysis utilizes a spectral database of fluorescence signatures of biological organisms and common interferents measured by Sandia for the Army's Edgewood Research and Development Engineering Center (ERDEC) and the Department of Energy's Chemical and Biological Non-proliferation (DOE CBNP) program. The analysis algorithms are based on algorithms developed by Sandia for an airborne UV LIF lidar system.
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