High-current electron optical design for reflective electron beam lithography direct write lithography
(Color online) Block and ray diagram of the second generation REBL column showing all major optical components along with the locations of the pupil and image planes.
(Color online) Photograph of the second generation REBL column installed on a test stand for evaluating column performance. The gun and illumination arm are on the right side of the column.
(Color online) Simulated and experimental energy spread for the REBL column. Simulation uses Munro’s IMAGE code for Coulomb interactions. Experimental energy spread is measured by varying the DPG surface potential to form a simple retarding energy analyzer.
(Color online) Simulation of projection blur for the REBL column as a function of the current at the wafer. Three different aperture sizes are shown: the smaller aperture gives better resolution at low currents due to reduced geometrical aberrations, the largest aperture gives the best resolution at high currents due to reduced Coulomb blur, but the middle aperture is optimum over the normal current range of interest.
Wafer plane image from the second generation REBL column projected onto a scintillating screen. The image is formed by the reflection of a fixed pattern DPG chip. The smallest features are 24 nm lines and spaces (measured at the wafer plane).
(Color online) Simulation of beam current as a function of the beam energy for a maximum blur of 41 nm. Also shown is the relative throughput, which has been corrected for the drop in resist sensitivity as beam energy increases.
(Color online) Simulation of energy spread in the illumination beam as a function of the illumination current. The round cathode uses a rectangular aperture at the intermediate image plane to shape the illumination, whereas the rectangular cathode shape directly defines the illumination profile.
YAG screen image of the emission intensity from a prototype rectangular cathode.
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