Influence of electron density distribution at the electron source in a projection exposure system

The influences of the size and the density distribution at the electron sou rce on the electron exposure characteristics in a projection lithography sy stem are studied. The individual electron trajectory is traced in a realist ic optical sq stem considering the Coulomb interaction effect among electro ns along with the lens aberration to discuss these effects quantitatively. The uniform, the Gaussian, and the ring density distributions are calculate d as the spatial distribution of the electron density at the source. Based on the results obtained above, the most preferable conditions for the elect ron sourer are clarified for the projection exposure system. A simple equat ion is obtained for estimating the most preferable diameter and the broadne ss of the ring. Lf the ring sourer is used in the projection electron optic al system, it is shown that the minimum displacement distance at the wafer surface can be largely improved, and it may be approximately 50 nm at the a cceleration voltage of 50 kV with the current density of 10 A/cm(2).