Mohsen Azadi

Isofocal dose based proximity effect correction tolerance to the effective process blur

The isofocal dose in electron beam lithography (EBL) is defined as the dose that results in the same feature size independent of the effective blur (blureff), which is the result of a combination of resist processing, spot size, beam focus, forward scattering, etc., that contributes to the final resist image. In other words, as blureff changes the same feature size is still obtained while using the same dose. This phenomenon is clearly demonstrated in EBL simulation when varying the blureff. In this work, the authors identify the isofocal dose for a given resist process consisting of 200 nm of ZEP520A from ZEON Chemicals atop a Si substrate using 300 nm line-space tower patterns with pattern densities ranging from 0% to 100% on an Elionix ELS-7500EX 50 keV EBL tool with a fixed 20 MHz clock at 200 pA with a 30 μm final aperture and a 20 nm beam step size. In this experiment, the dominant component of the blureff is the electron beam focus. By comparing line width measurements from tower patterns exposed w...