Bipolar extraction neutralization: Time resolved characterization

By switching the polarization of the screen and accelerator grid of a two g rid extraction system, an ion or electron beam can be extracted from the sa me gas discharge. Such ion source operation mode, called bipolar extraction neutralization (BEN), allows a filamentless current neutralization of elec trically insulated substrates. In this study BEN was used for a broad (12 c m), high current (0.36 A) ion beam from an electron cyclotron resonance ion source. The neutralization process is controlled by the duty cycle and fre quency of the electron extraction pulses. An electrostatic monitor was posi tioned in the vicinity of the sputter target and used for monitoring the be am plasma potential and control of the neutralization parameters. The beam potential and extraction grid currents are presented time resolved for neut ralization frequency from 20 to 80 kHz and duty cycle from 10% to 80%. This kind of monitoring allows not only control of the ion/electron extraction but also determination of the ion time of flight between the extraction gri d and the substrate. (C) 2000 American Institute of Physics. [S0034-6748(00 )65602-2].