Beam current control of an ECR ion source for medium current ion implanter

ECR ion sources in general have good properties such as long lifetime and high output of multiply charged ions although the dynamic range of beam current is quite narrow. An ECR ion source which can generate a wide range of beam current is developed for a medium current implanter. The source magnetic fields are produced by two solenoids each of which has field decoupling structure. Plasma density at the extraction slit can be changed by adjusting the current of one solenoid while a high density plasma is stably sustained near the microwave window with a constant current of the other solenoid. The beam current of B/sup +/ at target is controlled quickly from of 7 /spl mu/A to 2.5 mA by the current setting of one solenoid.