A modified broad beam ion source for low-energy hydrogen implantation

A modified broad beam ion source for low-energy hydrogen ion implantation of semiconductors is described. Based on a Kaufman type ion source two different solutions are presented: (a) an ion source with an extraction system consisting of two molybdenum grids with a low gas flow conductance reworked for hydrogen operation, and (b) a ten-grid mass separating ion beam system which enables the mass selection of H+, H-2(+), and H-3(+). The ion energy could be set in the range of 200-500 eV with a current density reaching from 1 to 100 mu A/cm(2). It is shown that at higher pressure the main ion created in the ion source is H-3(+) due to ion-molecule processes, whereas at lower pressure only H-2(+) and H+ are produced. Special consideration is given to the ion beam analysis of the two grid ion source operating in the 10(-3) mbar range allowing to explain the different peak structures by the potential distribution across the ion source and different charge transfer processes. In addition, the analysis reveals neutral and ionized collision products in the ion beam. The ten-grid mass separating ion source could be operated in the 10(-4) mbar range resulting in a nearly collision free ion beam which permits the generation of a mass separated hydrogen ion beam. (C) 1998 American Institute of Physics.