Global space charge effect in SCALPEL

The global space charge (SC) effect in SCALPEL electron beam lithography system is investigated. First order properties of the SC lensing action (defocus and magnification change) in SCALPEL type projection systems are analyzed using a simple analytical technique. Aberrations induced by the lenses and SC in the projection optics are evaluated numerically using a Monte Carlo code developed to calculate the combined effect of Coulomb interactions and lens aberrations in the charge particle projection systems. We found that the defocus and the magnification change induced by SC are functions of two parameters, the beam perveance and the SCALPEL aperture size, that are critical for the system performance. The strong correlation identified between the best focus plane location and the aberrations induced by SC indicates that the SC lensing action can be effectively compensated by simply adjusting either the wafer plane position or excitations of projection lenses.