Influence of Coulomb effects on electron projection lithography process

Abstract

Electron projection lithography (EPL) is an attractive candidate for next-generation lithography. In EPL, Coulomb effects consisting of a global space charge and stochastic Coulomb effect are a concern because of the huge beam current exposure required. We discuss the influence of the Coulomb effects in EPL. Proximity and Coulomb effects are known to degrade resolution and dose margin. To discriminate between the influence of Coulomb effects on exposure results from those of the proximity effect, we used complementary exposures. We found that a resolution of 1:1 L&S at a 6.9μA beam current on a wafer was 100nm and at a 1.3μA beam current was 65–70nm. These results roughly met specifications of the EPL system, NSR-EB1A. We found, however, that the beam blur varied within a subfield, and the difference between CD at 0.5 and 6.4μA at 100nm was 12nm due to the different beam blur, even if the space-charge effect was corrected by refocusing. To achieve accurate CD control, the proximity effect must thus be corrected considering beam blur distribution in the subfield.