COULOMB EFFECT IN CELL PROJECTION LITHOGRAPHY

Beam blurring due to Coulomb effects is very important in cell project ion lithography. This article reports on Coulomb effects in cell proje ction lithography by simulation and experiment, and shows some importa nt results. First, the Coulomb effect in a single cell is substantiall y uniform in conventional cell projection optics. Second, refocusing i s effective in reducing the space charge effect even in Koehler illumi nation with a Gaussian crossover. Third, the optimum cell size in the case of a large aperture percentage depends on the ratio of the total exposure time in the peripheral circuit to the total settling time in the memory cell mat. In addition, a modified mask technique is propose d to decrease the influence of Coulomb effects on throughput. (C) 1995 American Vacuum Society.