Optimization of secondary electron flood design for the production of low energy electrons

Modern high current implanters utilize secondary electron flood (SEF) or plasma electron flood (PEF) technology to provide charging control. Excessive negative charging may occur in the presence of electrons with a high energy distribution. We present a description for charge distribution within the ion beam, charge interaction at the device level, and optimization of an SEF design to allow only low energy electrons to reach the wafer. This results in a very wide operating window for varied primary currents. Performance improvements are quantified using charge to breakdown (Qbd) structures developed to characterize charging performance. We demonstrate that an optimized secondary electron flood design allows us to achieve a minimal gate oxide damage even under extreme conditions of ion implantation (dose, beam current).