Control of wafer charging during ion implantation: Issues, monitors and models

Charge control during ion implantation depends on the interaction of the ion beam plasma with the device wafer and other local sources of charged species. The key role of the net ion density, plasma electron temperature and plasma ion mass are discussed. The value of local monitoring of the current-voltage characteristics of the net plasma at the wafer surface with EEPROM sense and measurement devices is illustrated with effects of various charge control systems and the influence of resist patterning on the net current flow to the wafer. The special challenges of space charge control for sub-keV ion beams and the impact on local doping uniformity are also discussed.