Double‐aperture method of producing variably shaped writing spots for electron lithography

Edge definition in an electron‐beam lithography instrument may be improved by imaging an illuminated aperture instead of a Gaussian electron source, but such a system suffers from either slow throughput or large minimum feature size. A system has been constructed here in which an image of one aperture is projected onto a second, and both are imaged onto the writing surface. By changing the relative positions with an electrostatic deflection system, the size and shape of the writing spot may be changed within a few nanoseconds. Two square apertures can be used to give a writing spot of rectangular cross section with variable dimensions. Such an arrangement can be used directly in vector scan, and an example of a scheme for raster scan is described. Alternatively, an aperture of complicated shape is used so that the writing spot resembles four independent spots adjacent to each other. By using suitable electrostatic deflection, any combination of the four can be blanked off at any one time. A system employing this technique has been constructed, and simple patterns written on silicon wafers demonstrate a factor of four increase in speed over the Bell Laboratories EBES lithography instrument.