Beam purity control in the VIISta 810 implanter

Energy impurities in ion beams can result from dissociation of molecular ions or charge exchange by ions in the beam. Beam energy purity control in high and low energy implantation requires the removal of these unwanted components. Traditionally this is accomplished by using an electrostatic filter following mass analysis. In the Varian VIISta 810 200/300 mm medium current implanter a dual magnetic filter system is used to eliminate energy contamination. Moreover, unwanted beam elements are removed early in the beamline at low energy, and well away from the wafer. Low energy beam currents in VIISta 810 are enhanced by running the terminal in decel mode. Since there is no line of sight between the terminal and the wafer, energy contamination in decel mode is also eliminated. SIMS data will be presented to demonstrate the enhanced energy purity of the VIISta 810 beamline design.