We investigate a new technique for high current density beam formation called 3rd order imaging. This technique
has two advantages: 1) increasing the beam current without beam blurring, and 2) producing a desired beam shape, such
as a square or rectangle. Thus, it can significantly decrease writing times in Electron Beam Direct Writing (EBDW).
These advantages are realized by using a patterned beam-defining aperture (PBDA) whose patterned openings work with
the spherical aberration in the objective lens to generate the final beam shape. The PBDA transmits rays if they fall
within the desired shape at the wafer, while blocking rays which would fall outside the desired shape. We have obtained
beam line profiles and two-dimensional beam shapes experimentally. The 3rd-order imaging beam current density is
seven times larger than that of a beam shaped by the conventional aperture. The experimental beam profile and the
calculated result are in good agreement. The experimental two-dimensional shapes reproduce the calculated beam
shapes, thereby verifying the theory of 3rd-order imaging. This technique is a potential solution to break through the
technological impasse of high current density versus high resolution.