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24 March 2008 Experimental quantification of reticle electrostatic damage below the threshold for ESD
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The damage mechanisms that take place when a reticle is subjected to electrical stress by exposure to an electric field have been investigated by applying voltage directly to the structures in a special test reticle. Surface current was recorded at all levels of stress from 1V to 100V. The current/voltage characteristic was polarity dependent and exhibited increasing non-linearity as the feature spacing was reduced. Atomic Force Microscopy showed that the electrical stress caused EFM (Electric Field induced Migration of chrome), matching the damage seen in reticles stressed through induction by an external electric field. No ESD events were recorded, confirming that EFM is independent of ESD and that it occurs with lower electrical stress. The threshold for EFM was found to be five times lower than the previous estimate, starting at 1V with 1µm spacing. Damage caused by EFM was shown to be continuous, cumulative and the rate of CD degradation was measured to be from 3 to 6 nm per second.
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Gavin C. Rider and Thottam S. Kalkur "Experimental quantification of reticle electrostatic damage below the threshold for ESD", Proc. SPIE 6922, Metrology, Inspection, and Process Control for Microlithography XXII, 69221Y (24 March 2008);

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