Positional errors due to substrate charging in e-beam lithography tools

As computer logic and memory device dimensions shrink to submicron range the mask lithography tool placement accuracy becomes more critical. Charging effects in e-beam tools considered irrelevant in the past, today represent a large portion of the total error budget. Two such effects on glass substrates are described in this paper. The first is brought about by incomplete Cr coating of the edges, while the second is due to resist charging. It is shown that conductive coating of the edges is necessary if the exposed patterns fall closer than approximately 25 mm from the edge. Thin resist coatings less than 1.0 um can be tolerated when combined with Au mesh shielding techniques and application of electrostatic fields near the target. This gives the low energy secondary electrons a "harmless" path, reducing the charge accumulation on the resist surface.