Effect of an extractor electrode on ion beam focusing in a plasma sputter-type negative source

Abstract

In recent years, the focus of interest has been in to the production of negative ions due to its myriad applications in fields such as microelectronic manufacturing, nuclear and fusion research metal surface modification, isotope separation, ion-assisted thin film deposition, mass spectrometry and accelerator-based atomic and applied research among others. From among the numerous versatile means of negative ion production, the sputtering method has been utilized to great extent due to its relative ease in ion beam formation. One such facility that employs the above method is the multicusp plasma sputter-type negative ion source (PSNIS) developed by Mori, et al. and Alton, et al.
Recent studies conducted on the facility dealt more on the production of negative zirconium ions. However, results indicate a low beam current density that is inadequate for ion beam assisted thin film formation. This problem is resolved by incorporating beam manipulation components such as an electrostatic extractor and lens. The objective of this study is to investigate the effects of an electrostatic extractor electrode in ion beam transport. The desired effect is to obtain a high negative ion flux thereby improving the beam current density to significant levels appropriate for thin film formation. It is also important to produce a monoenergetic beam – a beam with the least presence of positive ions and very low energy negative ions. Other important considerations are the improvement of beam spot size and uniform energy spread.