Two-dimensional beam plasma parameter maps for secondary electron, plasma bridge, and plasma cell floods

The electron distribution (both density and energy) within and around an ion beam are very important in ion implanters for two reasons. The first deals with wafer charging which effects device yields, and the second deals with the defocusing effects of gradients in space potential, causing losses in transmission (especially in high perveance beams). An instrument has been developed capable of obtaining the J-V characteristic curves at all points within and around the beam while the beam is striking an insulating target (thereby simulating the worst case situation). This instrument consists of a linear array of current sensors (or "microfaraday") in back of two slits. By scanning the device across the beam, and by using various biasing arrangements of the slits and microfaraday, one can obtain two-dimensional maps of plasma parameters such as floating potential, electron temperature and plasma density. Data is compared from three types of electron floods: secondary emission, plasma bridge, and plasma cell. Besides showing how each is capable of reducing wafer charging, the data shows that in all cases, the interaction between the shower and beam plasma is qualitatively the same, enabling us to propose a single model explaining all three.