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Ultra low energy ion implantation with high beam current is required for shallow junction formation. Due to space charge limits in low energy ion beam transport, it is necessary to extract ion beams at higher energy (>1 kV) and decelerate them to a target energy as low as 100 eV near the process wafers. Energy contamination due to energetic neutral particles that result from charge exchanges between beam ions and bean-dine residual gas molecules before and during deceleration, increases proportionally with beamline pressure and is difficult to be prevented without sacrificing beam currents substantially. AIBT has developed a method or energy contamination control. Both electrical and magnetic fields are applied to the deceleration region so that the energetic neutral particles created before and during beam deceleration are guided to neutral beam blockers instead of the wafers. The energy contamination is negligible though the beamline pressure is as high as 1E-4torr. This method maximizes beam current performance at ultra low energy and gives easy implant control since the beamline pressure does not affect energy contamination level in our system.