Characteristic variation of exposure pattern in the cell-projection electron beam lithography

Electron beam cell-projection lithography is one of the most promising technologies to realize both demands of high-resolution and high-throughput in electron beam lithography process of LSI production. It is understood that the Coulomb interaction among electrons in the beam is the major critical issue for the technology. In an exposure of a series of line and space pattern in the optical system, the quality of the exposure pattern varies depending on the current density and the width of the line. Because of the Coulomb repulsion force among electrons, the pattern does not focus on the exact optical focal plane, but focus on a little farther. By adjusting the position of the specimen surface, the dearest pattern is obtained. Here, the distance to be adjusted is called the refocus length. The optimum refocus length for the pattern is obtained here in three methods, that is: (1) as the maximum number of electrons are in the designed pattern; (2) as the minimum exposure pattern width is obtained; and (3) as the maximum contrast of the exposure pattern is obtained. The relationship among these parameters are clarified quantitatively in the present study.