Novel ion beam extraction assembly with improved lifetime for high current, low energy ion implanters

In low energy, high current ion beam extraction, the use of relatively high suppression voltages is required to be able to increase the extraction gap in order to minimise arcing between the source and the extraction electrodes. The high local pressure and temperature within the electrode region, combined with relatively high suppression voltage causes insulator coating, and tracking which leads to premature failure of the insulators. This increases the downtime and reduces the productivity of the implanter. Laser Ion Mass Analysis (LIMA) carried out on various coated insulators showed that W deposits, presumably from the ion source, may be responsible for the failure of the insulators. Insulators have now been eliminated from the extraction region by developing a novel extraction assembly design using dual edge-welded bellows to provide the longitudinal and lateral motions needed for optimum beam tuning. The mechanical design is robust and takes into account the high thermal stability needed for stable high current beam extraction. Extensive tests have been undertaken on the “dual bellows” assembly and lifetimes well above 300 hours have regularly been obtained. Metal contamination tests on wafers implanted using the dual bellows extraction assembly in a 9500×R implanter have shown very low levels, well within the implanter specification