(Color online) Fogging is caused by multiple scatterings of electrons: (a) electrons from the primary beam are scattered in the resist, producing back-scattered and secondary electrons; these electrons scatter from the bottom of the objective lens, producing the next generation of secondaries; they in turn reach the resist and substrate and scatter there; (b) multiple scatterings produce exposure and charging far away from the intended exposure point.
(Color online) CHARIOT software was upgraded to simulate scattering precisely on a small area and cover large areas of the chamber: four tetrahedral meshes were constructed to cover scales from the nanometer sizes at the sample level to tens of millimeters at the chamber level. White arrows are showing area that have been magnified.
(Color online) Simulated trajectories of secondary electrons from the 3D target (seen as the bright point at the bottom, where trajectories are starting) near the ring electrode; a 100 V potential was added to the ring.
(Color online) Simulated distribution of absorbed energy. (a) The peak of absorbed energy is due to exposure by primary and backscattered electrons, the tail extending a few tens of mm is due to fogging; (b) the distribution of absorbed energy due to fogging only, well described by Gaussian, shown as a red line.
(Color online) Gaussian standard deviation w of the fogging range as a function of working distance. The absorbed energy and charging show slightly different values.
(Color online) Distribution of absorbed energy due to fogging at beam energies 1.5 kV and 50 kV.
(Color online) Distribution of absorbed energy due to fogging at various radii of the hole in the objective lens.
(Color online) Distribution of absorbed energy due to fogging throughout the resist thickness. The zero coordinate on the axis of resist depth corresponds to the upper surface of the resist. The increase of absorbed energy near the resist surface is attributed to a significant number of low energy electrons that cannot penetrate the full depth of the resist.
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